Use FooterPreference in AccountSyncSettings page

.Use the new FooterPreference and removed the old FooterPreferenceMixin
 from the AccountSyncSettings page.
.Add the ShadowAuthenticationHelper for commnon shadow util.

Fixes: 138978130
Test: manual test
Test: make RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.accounts
Change-Id: I93ae46b3b66e7e504320a9ed120ab7948dd06423