Remove unused methods and classes

This is a follow up CL to my previous CL [1], which logically reverted
IInputMethodManager from emulated sync IPCs to truly sync IPCs.

There are several methods and classes that are no longer actively used
after that revert CL.  This CL also removes those unused stuff until
we we actually start using them again.

Since those methods and classes are not used right now, there should
be no user/developer visible behavior change in this CL.

 [1]: If16ac0de536d9089eb04f6e07b1ee47378124658
      662b48b7

Bug: 192412909
Test: presubmit
Change-Id: I8666ac1399058b980e51e2459122b2f5f36c77b5