Revert "[ext-code-space] Enable external code space on x64 and desktop arm64"

This reverts commit e7ffb257.

Reason for revert: speculative revert because it might be causing 
these failures: https://ci.chromium.org/p/chromium/builders/ci/Deterministic%20Linux/32597

Original change's description:
> [ext-code-space] Enable external code space on x64 and desktop arm64
>
> This is a reland #2. The fixes were landed separately.
>
> Perf Sheriffs: this CL might regress some benchmarks while improving
> the others.
>
> Bug: v8:11880
> Change-Id: I397aef5ad5cce42ef189ee10b482805c90ec925a
> Cq-Include-Trybots: luci.v8.try:v8_android_arm64_compile_dbg
> Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3417000
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78817}

Bug: v8:11880
Change-Id: I74ec916267626433a060aa1b7804a4bfffeff269
Cq-Include-Trybots: luci.v8.try:v8_android_arm64_compile_dbg
Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3422640
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78837}

BUILD.gn

@@ -412,12 +412,7 @@ if (v8_enable_short_builtin_calls == "") {
       v8_current_cpu == "x64" || (!is_android && v8_current_cpu == "arm64")
 }
 if (v8_enable_external_code_space == "") {
-  # Can't use !is_android here, because Torque toolchain is affected by
-  # the value of this flag but actually runs on the host side.
-  v8_enable_external_code_space =
-      v8_enable_pointer_compression &&
-      (v8_current_cpu == "x64" ||
-       (target_os != "android" && v8_current_cpu == "arm64"))
+  v8_enable_external_code_space = false
 }
 if (v8_enable_single_generation == "") {
   v8_enable_single_generation = v8_disable_write_barriers