Remove unnecessary includes across the ads component. Remove verbose
per-method doc comments from BatAdsClientNotifierImpl, replacing them
with a class-level comment and an override group label. Delete copy and
move special member declarations from BatAdsObserver that were never
defined and cannot work with a non-copyable mojo::Remote. Fix the
AdsServiceDelegate class comment and remove the redundant explicit from
its constructor. Collapse trivial Act and Assert phases into a single
// Act & Assert expression in value util tests.
No behavioral changes.