[LoginDbDeprecationAndroid] Remove from about:flags and rename

The flag was enabled by default in M139 and can be cleaned up starting
in M140. Rename to allow gradual clean up over various days without
causing issues for canary users with outdated finch seeds.

Bug: 378653046
Change-Id: Ib517ccd364c54402721897cd3af76299d90e7f8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6679294
Auto-Submit: Victor Vianna <victorvianna@google.com>
Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Commit-Queue: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/main@{#1490711}