[SB] Update docs for AirplaneMode classes.

Thanks to the work on b/264539100, AirplaneModeRepository &
AirplaneModeInteractor *are* used to display the airplane mode icon
in the status bar.

Bug: 264539100
Flag: EXEMPT doc-only change
Test: m SystemUI
Change-Id: I278e9f8b6715a2d31d6c051ef6bd35479c576827