Revert "[build] Disable slow asserts for v8_enable_fast_mksnapshot"

This reverts commit 7a0d6a50.

Reason for revert: Breaks no-slow-assert builds.

Original change's description:
> [build] Disable slow asserts for v8_enable_fast_mksnapshot
> 
> Slow asserts double the time spent in mksnapshot. While we want them
> enabled on our bot builds, local builds should be fast and don't
> necessarily need them.
> 
> This also adds v8_enable_fast_mksnapshot as default in gm.py.
> 
> Bug: v8:7891,v8:6688
> Change-Id: I5ab1491f3396c4351de30dbbb80a81e2242c5db9
> Reviewed-on: https://chromium-review.googlesource.com/1116552
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#54074}

TBR=jkummerow@chromium.org,jgruber@chromium.org

Change-Id: I6b048e819846c4bd9a064f82e2f3c7609369cd33
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:7891, v8:6688
Reviewed-on: https://chromium-review.googlesource.com/1118138Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54077}

BUILD.gn

@@ -1059,7 +1059,6 @@ template("run_mksnapshot") {
 
     if (v8_enable_fast_mksnapshot) {
       args += [
-        "--no-enable-slow-asserts",
         "--no-turbo-rewrite-far-jumps",
         "--no-turbo-verify-allocation",
       ]

tools/dev/gm.py

@@ -119,7 +119,6 @@ symbol_level = 2
 use_goma = {GOMA}
 goma_dir = \"{GOMA_DIR}\"
 v8_enable_backtrace = true
-v8_enable_fast_mksnapshot = true
 v8_enable_slow_dchecks = true
 v8_optimized_debug = false
 """.replace("{GOMA}", USE_GOMA).replace("{GOMA_DIR}", str(GOMADIR))
@@ -132,7 +131,6 @@ symbol_level = 1
 use_goma = {GOMA}
 goma_dir = \"{GOMA_DIR}\"
 v8_enable_backtrace = true
-v8_enable_fast_mksnapshot = true
 v8_enable_verify_heap = true
 v8_optimized_debug = true
 """.replace("{GOMA}", USE_GOMA).replace("{GOMA_DIR}", str(GOMADIR))