Revert^2 "[res] Simplify overlayable support in OverlayReferenceMapper"

This reverts commit f4c0d181.

Reason for revert: fixing the null overlayable name crash

Original comment:
We don't have support for mulitple overlayable definitions per
package, and having that in the mock interface causes GC
pressure during boot for no reasons other than supporting test
inferfaces

Test: build + boot + \
  atest OverlayReferenceMapperTests AppsFilterImplTest
Flag: EXEMPT refactoring

Change-Id: Ifefd391fa69f52b1e1800a3171adf4b04cac5bae