simd/archsimd: remove BUG note about type parameter

simd/archsimd: remove BUG note about type parameter

After CL 742320, using vector type as type parameter now works.

Updates #77444

Change-Id: I4f8cd2c9c18e04efbc884cb57dfcf9f2b48306d8
Reviewed-on: https://go-review.googlesource.com/c/go/+/742400
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>