[dev.simd] internal/buildcfg: don't enable SIMD experiment by default

Preparing for merge to the main branch. Will reenable on the
branch.

Change-Id: I460dff3a5ceffb073f296098e76a35a90473de2f
Reviewed-on: https://go-review.googlesource.com/c/go/+/728241
TryBot-Bypass: Cherry Mui <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: cherrymui

src/internal/buildcfg/exp.go

@@ -84,7 +84,6 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
 		RegabiWrappers:        regabiSupported,
 		RegabiArgs:            regabiSupported,
 		Dwarf5:                dwarf5Supported,
-		SIMD:                  goarch == "amd64", // TODO: remove this (default to false) when dev.simd is merged
 		RandomizedHeapBase64:  true,
 		SizeSpecializedMalloc: true,
 		GreenTeaGC:            true,