Remove unused unique ID from GrProgramElement

Change-Id: I27140b378ad665c40f6edced1a655150ebd4842c
Reviewed-on: https://skia-review.googlesource.com/6800
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
2 files changed