Use Context.getSystemService(Class<T>) for InputMethodManager.

This is a mechanical replacement of Context.getSystemService(String)
with Context.getSystemService(Class<T>) when retrieving
InputMethodManager.  Note those are bundled code.  Hence we don't need
to make sure Build.VERSION.SDK_INT >= 23.

Change-Id: Icc64942ad8f11e44bf84f8d4fe476b2fdd1257f3