Drop some unuseful logs from IMM#doDump()

This CL does nothing but removes the following fields from

  adb shell dumpsys input_method

as they are not that useful.

 - InputMethodManager#mService
 - InputMethodManager#mMainLooper

Other than that, there is no behavior change in this CL.

Bug: 234882948
Test: adb shell dumpsys input_method
Change-Id: I82a2c37c19c28a10f52fd41581f3e11d9459f8f5