Fix lint errors around import lines in IMMS

This is a mechanical code clean-up. No behavior change is expected.

Fix: 113348139
Test: compile
Test: Run the following command to confirm that there remains no lint
      error regarding import lines:
   prebuilts/checkstyle/checkstyle.py -f frameworks/base/services/core/java/com/android/server/InputMethodManagerService.java
Change-Id: I90ce36ba94ed112baa3f6cb21edde2c2735311ff