selftests/bpf: Remove arena tests from DENYLIST.s390x

Now that the s390x JIT supports arena, remove the respective tests from
the denylist.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240701234304.14336-13-iii@linux.ibm.com

tools/testing/selftests/bpf/DENYLIST.s390x

@@ -4,6 +4,3 @@ exceptions				 # JIT does not support calling kfunc bpf_throw				       (excepti
 get_stack_raw_tp                         # user_stack corrupted user stack                                             (no backchain userspace)
 stacktrace_build_id                      # compare_map_keys stackid_hmap vs. stackmap err -2 errno 2                   (?)
 verifier_iterating_callbacks
-verifier_arena                           # JIT does not support arena
-arena_htab                               # JIT does not support arena
-arena_atomics