Add rule to ignore manifest.

When transitioning to androidx, android_core and androidx_core
have conflicting manifests, so we need be able to skip including one.


Bug: 1006427
Change-Id: I4fc4fac5e27cad7a3574773a62aaf0978f33f4ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1817335
Commit-Queue: benjamin joyce <bjoyce@google.com>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699028}