Stop restoring ENABLED_INPUT_METHODS

This CL logically reverts the following CL to stop restoring
Settings.Secure.ENABLED_INPUT_METHODS during the new device/user
setup.

 * If0104151b3526da6ecc669adde3119a239ecafeb
   7b9a28c7

This CL also partially reverts the following CL because part of that
CL is no longer necessary.

 * I94b4039c9f54c341aec72b62579be3dd8bd84dbb
   964943ab

In theory we should have been able to revert most of the following CL,
but other team it is already used by other projects so we cannot
revert it right now, unfortunately.

 * I01f5fafbbcfe3e3f5313829162ec011eaf2ad991
   2028ddaa

Reason for revert:
At high level, we doubt restoring
Settings.Secure.ENABLED_INPUT_METHODS still benefits restore
experience for the user.

 * Anecdotally almost all IMEs maintain enabled languages with their
   per-app settings such as SheredPreference.  This observation leads
   us to think that we should focus more on stabilizing per-app
   backup/restore scenario at least for IME migration scenarios.

 * The code is not that simple and cost to maintain it is not that
   low.  If we reverted this code, we could spend our resources for
   other tasks, including improving restore experience for the user.

 * Stopping restoring ENABLED_INPUT_METHODS reduces chances to
   conflict with what the device policy says [1].

 * We have had a strict rule about what IMEs can be enabled
   automatically, and the rule has been that only pre-installed IMEs
   can be automatically enabled by the system, unless some system
   components that have WRITE_SECURE_SETTINGS permission overrides it.
   Mechanically enabling an IME just because it was enabled in the
   previous device does not fit this model well.

 * Since Android O MR1, we also backup/restore user languages
   specified in the global settings [2].  The default selected IME
   should be able to automatically enable language support based on
   the restored system locales.

 [1]: DevicePolicyManager#setPermittedInputMethods()
 [2]: I1e6c7ba5b7abb6bde8b01ce0f647c04a5caa81a6
      0f19cc77

Fix: 72978240
Test: atest FrameworksCoreTests:android.provider.SettingsBackupTest
Test: atest FrameworksCoreTests:android.provider.SettingsValidatorsTest
Test: atest FrameworksCoreTests:com.android.internal.inputmethod.InputMethodUtilsTest
Change-Id: I122a8f69b2f75a9af85e14b66db764c5d153040e