Inline InputMethodManagerService.MethodCallback

This CL inlines InputMethodManagerService.MethodCallback as it is
semantically a single-method callback.

This is a mechanical refactoring.  There should be no behavior change.

Bug: 192412909
Test: presubmit
Change-Id: I3d110b905cc9b461d228735c2c5824ed54dceb08
1 file changed