Clean up InputMethodService

List of clean ups:
* Remove `mIsAutomotive` unused private field;
* Remove `isAutomotive` unused private method;
* Add javadoc to #onAppPrivateCommand empty public method
* Simplify unnecessary fully qualified names
  - 'ViewGroup.LayoutParams.MATCH_PARENT' due to existing static import 'android.view.ViewGroup.LayoutParams.MATCH_PARENT'
  - 'ViewGroup.LayoutParams.WRAP_CONTENT' due to existing static import 'android.view.ViewGroup.LayoutParams.WRAP_CONTENT'
* Replaced 'mHideNavBarForKeyboard' by a local variable.

Bug: 287045146
Test: m

Change-Id: Ie619defc632f2a4b76823a79e7f83471bdfb160e