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

This reverts commit fd608d18.

Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20UBSan%20-%20builder/838/overview

Original change's description:
> [ext-code-space] Enable external code space on x64 and desktop arm64
>
> Perf Sheriffs: this CL might regress some benchmarks while improving
> the others.
>
> Bug: v8:11880
> Change-Id: I857526d0971fc858b56126cbc276d9bd4157d71f
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3416244
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78774}

Bug: v8:11880
Change-Id: Ie1009824936a65790e743cbc01ca2e5bec5dec90
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3417432
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#78776}

BUILD.gn

@@ -412,9 +412,7 @@ if (v8_enable_short_builtin_calls == "") {
       v8_current_cpu == "x64" || (!is_android && v8_current_cpu == "arm64")
 }
 if (v8_enable_external_code_space == "") {
-  v8_enable_external_code_space =
-      v8_enable_pointer_compression &&
-      (v8_current_cpu == "x64" || (!is_android && v8_current_cpu == "arm64"))
+  v8_enable_external_code_space = false
 }
 if (v8_enable_single_generation == "") {
   v8_enable_single_generation = v8_disable_write_barriers