Remove rb_hash_ar_table_p

It's dead code and duplicate of RHASH_AR_TABLE_P.

hash.c

@@ -567,18 +567,6 @@ RHASH_TABLE_EMPTY_P(VALUE hash)
     return RHASH_SIZE(hash) == 0;
 }
 
-int
-rb_hash_ar_table_p(VALUE hash)
-{
-    if (FL_TEST_RAW((hash), RHASH_ST_TABLE_FLAG)) {
-        HASH_ASSERT(RHASH(hash)->as.st != NULL);
-        return FALSE;
-    }
-    else {
-        return TRUE;
-    }
-}
-
 void
 rb_hash_st_table_set(VALUE hash, st_table *st)
 {