Clean up button KDocs in remote-material3

Fixes copy-paste documentation in RemoteIconButton and RemoteTextButton:
- Corrects parameter and helper function docs in RemoteIconButton that
  referred to "text button" instead of "icon button".
- Fixes return type doc in RemoteTextButton.textButtonColors from
  TextButtonColors to RemoteTextButtonColors.
- Updates RemoteTextButtonColors class KDoc to reference
  RemoteTextButtonDefaults and removes unused imports.

Bug: 553908609
Test: ./gradlew :wear:compose:remote:remote-material3:checkApi :wear:compose:remote:remote-material3:lint
TAG=agy
CONV=3e429f1b-1b06-4e6d-97ed-608679feee5f

Change-Id: If490663273fa3a72af4c4aeddd7d4802d1a3872b