Remove bot_update assumption that HEAD is main

There is no need to override refs/heads/main to be HEAD. This may not
always be true, there is no benefits of doing so and it doesn't play
well with git_cache which will set HEAD to global default branch.

R=gavinmak@google.com

Bug: 1238084
Recipe-Manual-Change: build_limited
Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: infra
Change-Id: I21ab3463baaf7f86562ab0c65c06c3ac0962a08c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3088295
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

recipes/README.recipes.md

@@ -58,7 +58,7 @@ Recipe module to ensure a checkout is consistent on a bot.
 
 Wrapper for easy calling of bot_update.
 
-— **def [deapply\_patch](/recipes/recipe_modules/bot_update/api.py#531)(self, bot_update_step):**
+— **def [deapply\_patch](/recipes/recipe_modules/bot_update/api.py#527)(self, bot_update_step):**
 
 Deapplies a patch, taking care of DEPS and solution revisions properly.
     
@@ -95,7 +95,7 @@ Args:
     bot_update module ONLY supports one change. Users may specify a change
     via tryserver.set_change() and explicitly set this flag False.
 
-— **def [get\_project\_revision\_properties](/recipes/recipe_modules/bot_update/api.py#508)(self, project_name, gclient_config=None):**
+— **def [get\_project\_revision\_properties](/recipes/recipe_modules/bot_update/api.py#504)(self, project_name, gclient_config=None):**
 
 Returns all property names used for storing the checked-out revision of
 a given project.
@@ -111,7 +111,7 @@ Returns (list of str): All properties that'll hold the checked-out revision
 
 &emsp; **@property**<br>&mdash; **def [last\_returned\_properties](/recipes/recipe_modules/bot_update/api.py#47)(self):**
 
-&mdash; **def [resolve\_fixed\_revision](/recipes/recipe_modules/bot_update/api.py#459)(self, bot_update_json, name):**
+&mdash; **def [resolve\_fixed\_revision](/recipes/recipe_modules/bot_update/api.py#455)(self, bot_update_json, name):**
 
 Sets a fixed revision for a single dependency using project revision
 properties.

recipes/recipe_modules/bot_update/api.py

@@ -450,11 +450,7 @@ class BotUpdateApi(recipe_api.RecipeApi):
     if not patch_path or path != patch_path:
       return 'HEAD'
 
-    target_ref = self.m.tryserver.gerrit_change_target_ref
-    if target_ref == 'refs/heads/main':
-      return 'HEAD'
-
-    return target_ref
+    return self.m.tryserver.gerrit_change_target_ref
 
   def resolve_fixed_revision(self, bot_update_json, name):
     """Sets a fixed revision for a single dependency using project revision

recipes/recipe_modules/bot_update/examples/full.expected/deprecated_got_revision_mapping.json

@@ -62,7 +62,9 @@
       "--patch_ref",
       "https://chromium.googlesource.com/chromium/src@refs/heads/main:refs/changes/56/123456/7",
       "--revision",
-      "src@HEAD",
+      "src@refs/heads/main",
+      "--refs",
+      "refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {

recipes/recipe_modules/bot_update/examples/full.expected/no_apply_patch_on_gclient.json

@@ -64,7 +64,7 @@
       "--revision",
       "src@HEAD",
       "--revision",
-      "src/third_party/angle@HEAD",
+      "src/third_party/angle@refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {

recipes/recipe_modules/bot_update/examples/full.expected/tryjob_fail.json

@@ -62,7 +62,9 @@
       "--patch_ref",
       "https://chromium.googlesource.com/chromium/src@refs/heads/main:refs/changes/56/123456/7",
       "--revision",
-      "src@HEAD",
+      "src@refs/heads/main",
+      "--refs",
+      "refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {

recipes/recipe_modules/bot_update/examples/full.expected/tryjob_fail_patch.json

@@ -62,7 +62,9 @@
       "--patch_ref",
       "https://chromium.googlesource.com/chromium/src@refs/heads/main:refs/changes/56/123456/7",
       "--revision",
-      "src@HEAD",
+      "src@refs/heads/main",
+      "--refs",
+      "refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {

recipes/recipe_modules/bot_update/examples/full.expected/tryjob_fail_patch_download.json

@@ -62,7 +62,9 @@
       "--patch_ref",
       "https://chromium.googlesource.com/chromium/src@refs/heads/main:refs/changes/56/123456/7",
       "--revision",
-      "src@HEAD",
+      "src@refs/heads/main",
+      "--refs",
+      "refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {

recipes/recipe_modules/bot_update/examples/full.expected/tryjob_gerrit_angle.json

@@ -64,7 +64,7 @@
       "--revision",
       "src@HEAD",
       "--revision",
-      "src/third_party/angle@HEAD",
+      "src/third_party/angle@refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {

recipes/recipe_modules/bot_update/examples/full.expected/tryjob_gerrit_webrtc.json

@@ -64,7 +64,7 @@
       "--revision",
       "src@HEAD",
       "--revision",
-      "src/third_party/webrtc@HEAD",
+      "src/third_party/webrtc@refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {

recipes/recipe_modules/bot_update/examples/full.expected/tryjob_v8_head_by_default.json

@@ -64,7 +64,7 @@
       "--revision",
       "src@HEAD",
       "--revision",
-      "src/v8@HEAD",
+      "src/v8@refs/heads/main",
       "--disable-syntax-validation"
     ],
     "env": {