Revert "[sandbox] Sandboxify JSExternalObject external pointer"

This reverts commit efac35f3.

Reason for revert: Seems to be causing memory leaks: https://ci.chromium.org/ui/p/chromium/builders/try/linux_chromium_asan_rel_ng/1234545/overview

Original change's description:
> [sandbox] Sandboxify JSExternalObject external pointer
>
> Bug: v8:10391
> Change-Id: I6075a8fe3c201f9221149e0c54edf4fb191088da
> Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng,v8_linux_arm64_sim_heap_sandbox_dbg_ng
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3757342
> Commit-Queue: Samuel Groß <saelo@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#81924}

Bug: v8:10391
Change-Id: I8cd64fd0a85182781b04cd1e4619b69dfa512210
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng,v8_linux_arm64_sim_heap_sandbox_dbg_ng
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3780497
Auto-Submit: Samuel Groß <saelo@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81948}

include/v8-internal.h

@@ -374,7 +374,7 @@ constexpr uint64_t kAllExternalPointerTypeTags[] = {
   V(kNativeContextMicrotaskQueueTag,      unsandboxed, TAG(11)) \
   V(kEmbedderDataSlotPayloadTag,          unsandboxed, TAG(12)) \
   V(kCodeEntryPointTag,                   unsandboxed, TAG(13)) \
-  V(kExternalObjectValueTag,                sandboxed, TAG(14)) \
+  V(kExternalObjectValueTag,              unsandboxed, TAG(14)) \
   V(kCallHandlerInfoCallbackTag,          unsandboxed, TAG(15)) \
   V(kCallHandlerInfoJsCallbackTag,        unsandboxed, TAG(16)) \
   V(kAccessorInfoGetterTag,               unsandboxed, TAG(17)) \