[dev.simd] simd: rename stubs_amd64.go to ops_amd64.go

Change-Id: I42c3c8aed8bb19e251ae2aa0ee0f08e7796f1f4a
Reviewed-on: https://go-review.googlesource.com/c/go/+/686497
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/simd/stubs_amd64.go b/src/simd/ops_amd64.go
similarity index 100%
rename from src/simd/stubs_amd64.go
rename to src/simd/ops_amd64.go