build: Add support for PRODUCT_COPY_FILES_OVERRIDES

 * We may have a case where prebuilts need to be built from
   source instead based on an externalized config.
 * New directive takes a list of destination files to remove from
   PRODUCT_COPY_FILES so that other instructions can be supplied.

Change-Id: I7feff16440e54d1676ffddbbd96d5947efa43ede
(cherry picked from commit 7f90437176b02af5f59ac4f55345924da80f664f)