Remove InputMethodManagerService.LocalServiceImpl#mHandler

This field is now redundant with my previous CL [1].

 [1]: Id91dd600120e4981aa1d9005ce644728968430c9
      fffc0e53c62614c288e9e702d69e517db17dccd7

Bug: 112670859
Bug: 113877122
Test: atest CtsInputMethodTestCases CtsInputMethodServiceHostTestCases
Change-Id: I34b90ddd15c1cf743152c9028a3720150299273c
1 file changed