Remove duplicate booleans in BubbleUIInfo

We don't need both a boolean and a string label for the subpage and
checkbox, so simplify by having a non-empty label always be present.

Change-Id: I64f86e8b4378cedd715488832e87dd2ee4189b72
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4540340


Commit-Queue: Daniel Rubery <drubery@chromium.org>
Reviewed-by: Lily Chen <chlily@chromium.org>
Reviewed-by: Xinghui Lu <xinghuilu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1147339}