Fix lint warnings in IInputConnectionWrapper

This is a clean-up CL of IInputConnectionWrapper with no behavior
change.

As a preparation to move IInputConnectionWrapper into

  com.android.internal.inputmethod

this CL cleans up all the existing lint warnings in this file.

There should be no behavior change in this CL.

Bug: 192412909
Test: presubmit
Change-Id: I215437cc4e45f369af56e3d42fdc2bdc6d353a4f