Cleanup device_policy_size_tracking_*

device_policy_size_tracking_internal_enabled isn't used anywhere

device_policy_size_tracking_enabled was rolled out in V. It is exported,
so keeping the definition.

Bug: 335663055
Test: TH
Flag: EXEMPT flag cleanup
Change-Id: I59a5429154e972ae32e46d9bced81dbc9e7bd38d