Deprecate android.inputmethodservice.{Keyboard,KeyboardView}

This CL deprecates the following two classes.

 * android.inputmethodservice.Keyboard
 * android.inputmethodservice.KeyboardView

Most likely having these classes in the Android Framework does not
make much sense anymore, because basically it is just one
implementation of how keyboard-like UI can be implemented on top of
public Android APIs.  Source code of these classes have been available
as part os AOSP.  Thus it should not be that difficult for app
developers to have their own copy of these classes in their project or
re-implement a similar widget by themselves.

Fix: 116815596
Test: make -j checkbuild
Change-Id: Ie0cb0456c2cc4eacd4b188514508021774f60591