Revert "i965/fs: Allow scalar source regions on SNB math instructions."

Revert "i965/fs: Allow scalar source regions on SNB math instructions."

This reverts commit c1107cec44ab030c7fcc97c67baa12df1cc9d7b5.
Apparently the hardware spec text I quoted in the commit message was
outright lying about scalar source math being supported on SNB, the
hardware seems to load 32 contiguous bits of data for each channel
regardless of the regioning mode.  Fixes regressions in the following
CTS tests (which we didn't catch early due to CTS being temporarily
disabled in our CI system):

   es2-cts.gtf.gl.atan.atan_vec3_frag_xvary
   es2-cts.gtf.gl.cos.cos_vec2_frag_xvary
   es2-cts.gtf.gl.atan.atan_vec2_frag_xvary
   es2-cts.gtf.gl.pow.pow_vec2_frag_xvary_yconsthalf
   es2-cts.gtf.gl.cos.cos_float_frag_xvary
   es2-cts.gtf.gl.pow.pow_float_frag_xvary_yconsthalf
   es2-cts.gtf.gl.atan.atan_vec3_frag_xvaryyvary
   es2-cts.gtf.gl.pow.pow_vec3_frag_xvary_yconsthalf
   es2-cts.gtf.gl.cos.cos_vec3_frag_xvary
   es2-cts.gtf.gl.atan.atan_vec2_frag_xvaryyvary

Cc: mesa-stable@lists.freedesktop.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96346
Reported-by: Mark Janes <mark.a.janes@intel.com>
Acked-by: Matt Turner <mattst88@gmail.com>