Merge pull request #5134 from shuujii/fix-that-large-integer-is-not-GCed-with-Word-boxing

Fix that large integer is not GCed with Word-boxing

src/gc.c

@@ -782,7 +782,6 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
   switch (obj->tt) {
     /* immediate - no mark */
   case MRB_TT_TRUE:
-  case MRB_TT_INTEGER:
   case MRB_TT_SYMBOL:
     /* cannot happen */
     return;