i965: Remove "single threaded" INTEL_DEBUG mode.

i965: Remove "single threaded" INTEL_DEBUG mode.

According to the docs for 3DSTATE_PS (Gen7+) and 3DSTATE_WM (Gen6),
there is a platform dependent value for the minimum number of pixel
shader threads.  It may also vary based on whether WIZ Hashing is on.

For example, Ivybridge requires at least 4 threads if WIZ hashing is
disabled, and 8 if it's enabled.  Programming it to use less threads is
illegal.  Sandybridge appears to have similar restrictions.

So on newer platforms, INTEL_DEBUG=sing will probably just hang the GPU.
Rather than try to patch it up for newer platforms and extend it to
support geometry shaders, just remove it as it isn't that useful anyway.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>