Revert "[ptr-compr] Temporarily disable 31 bit Smis on 64-bit architectures"

This reverts commit 64c09f67.

Reason for revert: We already support up to max int32 sized TypedArrays
regardless of the smi size, so the chromium:1009439 issue should no longer be a blocker.

Original change's description:
> [ptr-compr] Temporarily disable 31 bit Smis on 64-bit architectures
>
> The reason is to unblock M79 blocked by chromium:1009439 while full
> solution is not ready yet.
>
> This CL will be reverted after the M79 branch point.
>
> Bug: v8:9767, chromium:1009439
> Change-Id: I5302d86fe953ecd94d9a4bba0d29c807b7b9d703
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1862554
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64286}

Bug: v8:9767, chromium:1009439
Change-Id: I92c43c8b27feb4f99e948bca03551e3e0316f2b5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1916692Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64971}

BUILD.gn

@@ -104,7 +104,7 @@ declare_args() {
 
   # Enable pointer compression (sets -dV8_COMPRESS_POINTERS).
   v8_enable_pointer_compression = ""
-  v8_enable_31bit_smis_on_64bit_arch = false
+  v8_enable_31bit_smis_on_64bit_arch = true
 
   # Sets -dOBJECT_PRINT.
   v8_enable_object_print = ""