Revert "[flags] Enable freezing of flags"

This reverts commit 1ed7d0b8.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Blink%20Linux%20Future/13719/overview

Original change's description:
> [flags] Enable freezing of flags
>
> This enables the --freeze-flags-after-init flag globally. Note that
> tests, fuzzers, Node and other still explicitly disable the flag. The
> chrome renderer process and default d8 execution will have it enabled
> though.
>
> R=​cbruni@chromium.org
>
> Bug: v8:12887
> Change-Id: I9a15ef64227e5e6e04779d8d671a2c50d99c9097
> Cq-Include-Trybots: luci.v8.try:v8_linux_blink_rel
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695264
> Reviewed-by: Camillo Bruni <cbruni@chromium.org>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#81214}

Bug: v8:12887
Change-Id: I63c45d4b026345d95a5de179600df960eae8ca0a
Cq-Include-Trybots: luci.v8.try:v8_linux_blink_rel
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3707280
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81218}

src/flags/flag-definitions.h

@@ -1877,7 +1877,7 @@ DEFINE_BOOL(
     "Fuzzers use this flag to signal that they are ... fuzzing. This causes "
     "intrinsics to fail silently (e.g. return undefined) on invalid usage.")
 
-DEFINE_BOOL(freeze_flags_after_init, true,
+DEFINE_BOOL(freeze_flags_after_init, false,
             "Disallow changes to flag values after initializing V8")
 
 // mksnapshot.cc