Remove some redundant macro definitions from gc_atomic_ops.h

Remove some redundant macro definitions from gc_atomic_ops.h
(fix commit 46a2411)

* include/private/gc_atomic_ops.h [GC_BUILTIN_ATOMIC] (AO_HAVE_load,
AO_HAVE_store, AO_HAVE_store_release_write): Remove.
* include/private/gc_atomic_ops.h [GC_BUILTIN_ATOMIC && AO_REQUIRE_CAS]
(AO_HAVE_compare_and_swap): Likewise.
* include/private/gc_atomic_ops.h [!GC_BUILTIN_ATOMIC]: Add comment.
* include/private/gc_priv.h (word_ptr_ao_u): Replace
"ifdef AO_HAVE_load" to "ifdef PARALLEL_MARK".
* tests/test_atomic_ops.c [AO_HAVE_compare_and_swap_release] (main):
Do not check whether AO_REQUIRE_CAS and AO_HAVE_compare_and_swap are
defined.
* typd_mlc.c [GC_FORCE_INCLUDE_ATOMIC_OPS || GC_BUILTIN_ATOMIC]
(include gc_atomic_ops.h): Do not check whether AO_HAVE_load_acquire
is defined.