Remove a redundant param in getDefaultEnabledImes

With the previous CL [1], systemReady parameter in
InputMethodUtils.getDefaultEnabledImes() is guaranteed to be true.
Hence this CL removes that parameter. There should be no behavior change
in this CL.

 [1]: I5b37c450db4b25b3e635b6d634293a34eec8b9d4
      7924782c

Test: adb shell am instrument -w -e class com.android.internal.inputmethod.InputMethodUtilsTest com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Bug: 32343335
Change-Id: Ia14d12a4e21d0e2e22bfe0bd8d496f48058c5525