i965: Remove block arg from foreach_inst_in_block_*_starting_from

i965: Remove block arg from foreach_inst_in_block_*_starting_from

Since 49374fab5d793 these macros no longer actually use the block
argument. I think this is worth doing to make the macros easier to use
because they already have really long names and a confusing set of
arguments.

Reviewed-by: Matt Turner <mattst88@gmail.com>