libgenlock: Remove <linux/libgenlock.h> include

Summary: This isn't a UAPI header, and it's no longer needed by libgenlock.

Test Plan: verified here

Reviewers: randall.rushing, jriordan001

Differential Revision: http://review.codefirex.com/D267

Change-Id: Ib93053b416461511f9a6f35d3194aa223cc40c04
Signed-off-by: DHOMD <DHO@dho.im>