i965/fs: Stop trying to hack around MRF dep chains on gen7+ LIFO scheduling.

i965/fs: Stop trying to hack around MRF dep chains on gen7+ LIFO scheduling.

This was a hack to avoid choosing to schedule all texturing before
consumption of any texture results due to the way dependency chains worked
out in the presence of MRFs.  On gen7, we don't have MRFs, so the problem
doesn't apply, and this was just badly constraining our scheduling.

total instructions in shared programs: 1615306 -> 1612534 (-0.17%)
instructions in affected programs:     9958 -> 7186 (-27.84%)
GAINED:                                259
LOST:                                  9

Reviewed-by: Matt Turner <mattst88@gmail.com>