Revert "Free the original pointer if `realloc` failed."

This reverts commit 9cdf439d.

src/gc.c

@@ -225,10 +225,15 @@ mrb_realloc(mrb_state *mrb, void *p, size_t len)
   p2 = mrb_realloc_simple(mrb, p, len);
   if (len == 0) return p2;
   if (p2 == NULL) {
-    mrb_free(mrb, p);
+    if (mrb->gc.out_of_memory) {
+      mrb_raise_nomemory(mrb);
+      /* mrb_panic(mrb); */
+    }
+    else {
       mrb->gc.out_of_memory = TRUE;
       mrb_raise_nomemory(mrb);
     }
+  }
   else {
     mrb->gc.out_of_memory = FALSE;
   }