Deleting a buffer that is bound to a VAO should act as if
the application unbound the buffer. Unbinding the buffer
should update relevant validation caches. But we were
missing the logic that updates the validation caches.

This CL adds the necessary cache updates. It does not include a
regression test. The test was causing an unrelated regression that is
going to be a bit longer. It should not block this fix.

Bug: chromium:943538
Change-Id: Ib073cd07a230ca073a5b14bc054e961158a0097d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1536491
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
(cherry picked from commit f7f15ac2)
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1556697Reviewed-by: Jamie Madill <jmadill@chromium.org>