Unextract InputMethodManagerService#startInputInnerLocked()

With my previous CL [1], IMMS#startInputInnerLocked() is called only
from IMMS#startInputUncheckedLocked().  By unextracting
IMMS#startInputInnerLocked() again, it would be much easier for us to
understand what IMMS#startInputUncheckedLocked() is actually doing.

To decouple actual behavior change from cosmetic code refactorings,
this CL does nothing except for merging IMMS#startInputInnerLocked()
into IMMS#startInputUncheckedLocked().

There should be no behavior change.  Non trivial behavior
simplifications will be done in subsequent CLs.

 [1]: I52f6c4cd1e02be3a59e9a87e33b0a44f4ba8d80b
      f91a2b10

Bug: 117730713
Test: atest ActivityManagerMultiDisplayTests
Test: atest CtsInputMethodTestCases CtsInputMethodServiceHostTestCases
Test: atest FrameworksCoreTests:android.view.inputmethod.InputMethodManagerTest
Change-Id: I71e259fa447dd06ff02b9ef8c958dc70bbce86ea