Fix lint warnings under services/tests/servicestests/src/com/android/server/inputmethod/

This is a mechanical refactoring.  There should be no change regarding
what's asserted in IME tests implemented in FrameworksServicesTests.

Bug: 171827834
Test: atest FrameworksServicesTests:com.android.server.inputmethod
Test: prebuilts/checkstyle/checkstyle.py \
        -f frameworks/base/services/tests/servicestests/src/com/android/server/inputmethod/ \
        | grep .java:
Change-Id: I448a6332a929e5a70b49071a76364bf3bcb4ac89