ParseAndClassifyIdentifier cannot result in invalid assignment patterns, so
don't check for them.

Change-Id: I038c651502e10d17b2da1c21527ef1b9e4cd16ea
Reviewed-on: https://chromium-review.googlesource.com/c/1270916
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56489}