Revert "Enable 31bit Smis everywhere"

This reverts commit c1bf25bb.

Reason for revert: We got many regressions:

https://chromeperf.appspot.com/group_report?rev=58157

Original change's description:
> Enable 31bit Smis everywhere
> 
> This is a experiment to see how performance is impacted. If we tank
> too much, we can revert this change.
> 
> Change-Id: I01be33f5dd78aee6a5beecdc62adbaa6c3850eb1
> Bug: v8:8344
> Reviewed-on: https://chromium-review.googlesource.com/c/1355279
> Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#58157}

TBR=jarin@chromium.org,sigurds@chromium.org,ishell@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:8344
Change-Id: I407cb99743a08452edcecfc2e945ef98509e8d32
Reviewed-on: https://chromium-review.googlesource.com/c/1375911Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58227}

BUILD.gn

@@ -101,6 +101,7 @@ declare_args() {
 
   # Enable pointer compression (sets -dV8_COMPRESS_POINTERS).
   v8_enable_pointer_compression = false
+  v8_enable_31bit_smis_on_64bit_arch = false
 
   # Interpreted regexp engine exists as platform-independent alternative
   # based where the regular expression is compiled to a bytecode.
@@ -346,6 +347,9 @@ config("features") {
   if (v8_enable_pointer_compression) {
     defines += [ "V8_COMPRESS_POINTERS" ]
   }
+  if (v8_enable_31bit_smis_on_64bit_arch) {
+    defines += [ "V8_31BIT_SMIS_ON_64BIT_ARCH" ]
+  }
   if (v8_enable_object_print) {
     defines += [ "OBJECT_PRINT" ]
   }

include/v8-internal.h

@@ -92,7 +92,11 @@ static_assert(
     "Pointer compression can be enabled only for 64-bit architectures");
 #endif
 
+#if defined(V8_COMPRESS_POINTERS) || defined(V8_31BIT_SMIS_ON_64BIT_ARCH)
 typedef SmiTagging<kApiIntSize> PlatformSmiTagging;
+#else
+typedef SmiTagging<kApiSystemPointerSize> PlatformSmiTagging;
+#endif
 
 const int kSmiShiftSize = PlatformSmiTagging::kSmiShiftSize;
 const int kSmiValueSize = PlatformSmiTagging::kSmiValueSize;