Reland "Delete lots of svn logic from bot_update"

This is a reland of 082267a6
which was reverted in 4dcad385

BUG=472386

Review-Url: https://codereview.chromium.org/2325513002

tests/bot_update_coverage_test.py

@@ -37,7 +37,6 @@ DEFAULT_PARAMS = {
     'revision_mapping': {},
     'apply_issue_email_file': None,
     'apply_issue_key_file': None,
-    'buildspec': False,
     'gyp_env': None,
     'shallow': False,
     'runhooks': False,
@@ -192,14 +191,6 @@ class BotUpdateUnittests(unittest.TestCase):
     bot_update.ensure_checkout(**self.params)
     return self.call.records
 
-  def testBasicBuildspec(self):
-    self.params['buildspec'] = bot_update.BUILDSPEC_TYPE(
-        container='branches',
-        version='1.1.1.1'
-    )
-    bot_update.ensure_checkout(**self.params)
-    return self.call.records
-
   def testBasicShallow(self):
     self.params['shallow'] = True
     bot_update.ensure_checkout(**self.params)