Remove resources.apk from ZipSet when removing overlay

When a theme that is currently applied is updated, the resources.apk
prior to the update remains in the AssetManager ZipSet and is still
used when loading themed assets.  This patch removes the resources.apk
from the ZipSet so that the new one can be correctly loaded in.

Change-Id: I1c9373fa2dd7310a908a1c806c44aadb4d231a4a
REF: THEMES-639