Remove duplicated startInputUncheckedLocked invocation

As CL[1] removed unused "debug.optimize_startinput" flag logic in
IMMS#startInputOrWindowGainedFocusInternalLocked, we can even remove
duplicated startInputUncheckedLocked invocation to simpfy the code
block of the input didn't start part.

Note that this CL is a mechanical code refactoring, it should not have
any behavior change.

[1]: Ie7b09f16e517c0550ac495a8a8c8ef20abb6938e

Bug: 171827834
Test: atest CtsInputMethodTestCases
Change-Id: I8fbb2c6ad4dfbd8388d1780375f53fd750ebd83e