Hide setPolicyDataEnabled

This method was made into a SystemApi for R since
Telephony was going mainline.  The Telephony team
has a more robust solution as other similar APIs were
needed.  Since we are not going mainline, it makes
the most sense to wait for full solution.

Bug: 148165897
Bug: 146654731
Test: make \ flash
Change-Id: I5b38694acf3887e4f3ea2ab725b57fe4be9d5626