Remove neverallow rules for framework-mediaprovider

We actually want some targets (in particular, the MediaProvider apk)
to link against framework-mediaprovider.

The gist of what the neverallow rule achieves (disallow general use)
is achieved equally well with visibility rules, which
framework-mediaprovider already has.

Bug: 152891096
Test: m nothing
Change-Id: Ic4b0a571985b9ad1dfdd56d45035f224a622700e