Use FooterPreference in xml explicitly

Removed the FooterPreferenceMixin from the BluetoothDashboardFragment page.

Fixes: 139459430
Test: manual test
Test: make RunSettingsRoboTests ROBOTEST_FILTER=com.android.settings.connecteddevice
Change-Id: I8a8b6ba656405f938e203e20e5973c1560c3a35a
2 files changed