i965: remove cache_aux_free_func array

i965: remove cache_aux_free_func array

There is only one function that can be called, which is well known at
compilation time.

The abstraction used here seems unnecessary, so let's use a direct call
to brw_stage_prog_data_free() when appropriate, cut down the size of
struct brw_cache.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>