glamor: don't reset the GLSL program

glamor: don't reset the GLSL program

We don't use fixed function rendering, so there is no need to reset
the program at all.  This lets the driver avoid checking for state
changes between draw calls when we rebind the same program.

Improves xephyr x11perf -f8text performance by 6.03062% +/- 1.64928%
(n=20)

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>