Simplify IMMS#calledFromValidUserLocked()

With my previous CL [1], IMMS#calledFromValidUserLocked() now always
gets called with the same parameter.  Let's simplify it.

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

 [1]: Ieb94ed14698ee2669adc5fb2ea0e93c7d0e09e8b
      716897ce

Bug: 34886274
Test: atest CtsInputMethodTestCases CtsInputMethodServiceHostTestCases
Change-Id: I571db5a648ddf8b35caad3d3b64549b7cc067d14