Delete hiddenapi-p-light-greylist.

It's not used, and there is no reason to keep it now that P has been
pushed to AOSP.

Test: N/A
Change-Id: Ib025116032bdb215dba5b51de4c7ea8ad7dd10d5
Merged-In: I51bf94b736cae57780708a70947511c409a2dfb6