Deprecate /factory

After Treblized, AOSP do not handle /factory folder. Also, AOSP
does not mount any partition to /factory. /factory has no possibility
to have any content. For factory purpose, it can be implemented in
vendor.

Bug: 177280838
Test: na
Change-Id: I0a2537336c2ef1efbad3e4f9e876aeaa607bc737