Revert "Enable background merging of deserialized scripts"

This reverts commit f388f96f.

Reason for revert: Crashes in canary (https://crbug.com/1360024)

Original change's description:
> Enable background merging of deserialized scripts
>
> This can save memory in cases where multiple frames in a process use the
> same script, with sufficient time between loads that the script's
> top-level SharedFunctionInfo is no longer present in the compilation
> cache. Merging is relatively fast; it generally takes about one tenth as
> long as deserialization.
>
> Bug: v8:12808
> Change-Id: I7366a51f1d2ca6a9f551cdf2bdbe0441450cf1bb
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3868088
> Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82920}

Bug: v8:12808
Change-Id: If160173afaab351d995ddcf4b60d6efe656cf70b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3871208
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#82983}

src/flags/flag-definitions.h

@@ -475,6 +475,8 @@ DEFINE_WEAK_IMPLICATION(future, short_builtin_calls)
 #endif
 DEFINE_WEAK_NEG_IMPLICATION(future, write_protect_code_memory)
 DEFINE_WEAK_NEG_IMPLICATION(future, use_map_space)
+DEFINE_WEAK_IMPLICATION(
+    future, merge_background_deserialized_script_with_compilation_cache)
 
 DEFINE_BOOL_READONLY(dict_property_const_tracking,
                      V8_DICT_PROPERTY_CONST_TRACKING_BOOL,
@@ -1537,7 +1539,7 @@ DEFINE_BOOL(stress_background_compile, false,
 DEFINE_BOOL(concurrent_cache_deserialization, true,
             "enable deserializing code caches on background")
 DEFINE_BOOL(
-    merge_background_deserialized_script_with_compilation_cache, true,
+    merge_background_deserialized_script_with_compilation_cache, false,
     "After deserializing code cache data on a background thread, merge it into "
     "an existing Script if one is found in the Isolate compilation cache")
 DEFINE_BOOL(disable_old_api_accessors, false,