Cleanup of AccessibilityUtil#hasValueInSettings

Settings should now be able to directly use the equivalent ShortcutUtils functions,
so the unnecessary code is being removed from AccessibilityUtil.
This does cause much behavior to depend on A11yManager instead of Settings.Secure,
so several tests need their conditions updated.

Test: atest com.android.settings.accessibility
Flag: EXEMPT internal refactoring
Bug: 367414968

Change-Id: I95f81f7d78b074def0fe2d1e01f60ceb7e142dac