NIR does not have these instructions.  TGSI and Mesa IR both implement
them using < and >=, repsectively.  Removing them deletes a bunch of
code and means I don't have to add code to the SPIR-V generator for
them.

v2: Rebase on 2+ years of change... and fix a major bug added in the
rebase.

   text	   data	    bss	    dec	    hex	filename
8255291	 268856	 294072	8818219	 868e2b	32-bit i965_dri.so before
8254235	 268856	 294072	8817163	 868a0b	32-bit i965_dri.so after
7815339	 345592	 420592	8581523	 82f193	64-bit i965_dri.so before
7813995	 345560	 420592	8580147	 82ec33	64-bit i965_dri.so after

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>