The used flag was redundant with the index (which used MAXUINT). The
name was redundant with the stored uniform. Removing these gives a
very minor performance speed up when iterating and retrieving
uniform locations.

BUG=angleproject:1390

Change-Id: Ieeccdff7c131e1359e754e246d3648b73aad5baf
Reviewed-on: https://chromium-review.googlesource.com/659224
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>