glsl: Remove hash table from ir_set_program_inouts pass.

glsl: Remove hash table from ir_set_program_inouts pass.

Back when ir_var_in and ir_var_out signified both function parameters
and shader input/outputs, we had trouble distinguishing the two when
looking at a dereference.  Now that we have separate ir_var_shader_in
and ir_var_shader_out modes, we can determine this easily.

Removing the hash table saves memory and CPU overhead.

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