core-utils: Remove $(PERSIST_MOUNT_POINT)

Dependency on $(PERSIST_MOUNT_POINT) but missing
"$(TARGET_ROOT_OUT)/persist", lead to retrigerring kati and
Ninja build, and a re-packaging of vendor.img, many modules
and zip files in Null incremental build.
Remove $(PERSIST_MOUNT_POINT) because it is not mounted

Change-Id: I65eb3bd4674a50f2b7c0aed15ca4f52a65dd9f21
1 file changed