i965: Fix KHR_blend_equation_advanced with some render targets.

i965: Fix KHR_blend_equation_advanced with some render targets.

This reverts two bogus and seemingly useless changes from the commits
referenced below, which broke KHR_blend_equation_advanced (and
EXT_shader_framebuffer_fetch_non_coherent which wasn't exposed yet)
for any kind of render target surface that would cause the
get_isl_surf() call in brw_emit_surface_state() to do anything useful
(notice how the result of get_isl_surf() is completely ignored by the
caller right now), as was the case while using those extensions with
1D array or 3D framebuffers in particular.

Fixes: f5859b45b1686e8116380d87 "i965/miptree: Switch remaining surfaces to isl"
Fixes: bf24c3539e4b6989512968ca "i965/miptree: Clean-up unused"
Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Plamena Manolova <plamena.manolova@intel.com>