[infra] Remove unused test declarations.

The chrome_public_test_vr_apk-ddready-* targets are unused and reference
non-existent mixins. Removing them is necessary for a change that will
enforce the existence of referenced mixins.

Change-Id: I98064d514af2d1295f037e9679696d3bf9261e67
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5251257
Auto-Submit: Garrett Beaty <gbeaty@google.com>
Reviewed-by: Stephanie Kim <kimstephanie@google.com>
Commit-Queue: Stephanie Kim <kimstephanie@google.com>
Cr-Commit-Position: refs/heads/main@{#1254227}