mjit_worker.c: emphasize free_list of compact_units [ci skip]

In https://bugs.ruby-lang.org/issues/14867#note-98, it's considered
useless at once. So I emphasized the necessity of it in the comment.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65477 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

mjit_worker.c

@@ -178,7 +178,7 @@ int mjit_call_p = FALSE;
 static struct rb_mjit_unit_list unit_queue = { LIST_HEAD_INIT(unit_queue.head) };
 /* List of units which are successfully compiled. */
 static struct rb_mjit_unit_list active_units = { LIST_HEAD_INIT(active_units.head) };
-/* List of compacted so files which will be deleted in `mjit_finish()`. */
+/* List of compacted so files which will be cleaned up by `free_list()` in `mjit_finish()`. */
 static struct rb_mjit_unit_list compact_units = { LIST_HEAD_INIT(compact_units.head) };
 /* The number of so far processed ISEQs, used to generate unique id.  */
 static int current_unit_num;