Improve Controls Core API docs 3 (#33391)

Deleted XML documentation files for several Microsoft.Maui.Controls
types, including CarouselView, GridItemsLayout, and related event args.
This likely reflects a move to a new documentation system or a cleanup
of unused files.

Follow up from #33243 and #33240

With this PR we also remove the diagnostics code for missing API docs
from NoWarn so that we will be notified when something is missing in the
future.

Author: jfversluis