Remove a dependency on IMMS#getCurrentImeUserIdLocked()

This is a mechanical refactoring CL to remove the dependency on

  InputMethodManagerService#getCurrentImeUserIdLocked()

from

  InputMethodBindingControllerTest

without changing any test expectation.

Bug: 350386877
Test: atest FrameworksInputMethodSystemServerTests
Flag: TEST_ONLY
Change-Id: I37fb73b112cab80d68636184c0ddbec1d883d90c