Stop using InputMethodUtils.isValidSystemDefaultIme

This is a follow up CL for a recent attempt to minimize
the number of default enabled IMEs.
- part1: I831502db502f4073c9c2f50ce7705a4e45e2e1e3
- part2: Ife93d909fb8a24471c425c903e2b7048826e17a3
- part3: I6571d464a46453934f0a8f5e79018a67a9a3c845
- part4: I871ccda787eb0f1099ba3574356c1da4b33681f3

In the above changes,
InputMethodUtils.isValidSystemDefaultIme was deprecated in favor
of InputMethodUtils.isSystemImeThatHasSubtypeOf.

With this CL, InputMethodUtils.isValidSystemDefaultIme is not
used by the setting app anymore and we can remove that method
from InputMethodUtils finally.

This is a pure code refactoring with preserving the current
logic. Hence no behavior change is intended.

Change-Id: Ie96b0d17745735db63eebe6fe1654f32d9b9a170