i965: Eliminate brw_set_conditionalmod from the Gen4-5 compilers.

i965: Eliminate brw_set_conditionalmod from the Gen4-5 compilers.

With the predication changes eliminated, all this does is set the
conditional modifier on a single instruction.  Doing that directly is
easy, and avoids mucking about with default state.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>