i965: Remove old BSpec reference from BLORP's 3DSTATE_WM/PS packets.

i965: Remove old BSpec reference from BLORP's 3DSTATE_WM/PS packets.

The Sandybridge code had a citation for the range of the "Maximum Number
of Threads" field, and the Ivybridge code just mentioned the "BSpec" in
general.  That's documented in the obvious place, so people can find it
without a spec reference.

The real value of the comment is to say "we tried zero, and it exploded,
so program it to a valid number even if pixel shading is off."

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>