Remove dead code in rb_hash_replace

We now always copy the ST table, so we don't need to initialize the ST
table of hash when hash2 is empty.

hash.c

@@ -2933,11 +2933,6 @@ rb_hash_replace(VALUE hash, VALUE hash2)
         rb_gc_writebarrier_remember(hash);
     }
 
-    if (RHASH_EMPTY_P(hash2) && RHASH_ST_TABLE_P(hash2)) {
-        /* ident hash */
-        hash_st_table_init(hash, RHASH_TYPE(hash2), 0);
-    }
-
     return hash;
 }