storage/reflink: omit redundant comment

The is_dirty() one-liner is defined right above.

(cherry picked from commit 9c9d71c)

qubes/storage/reflink.py

@@ -206,7 +206,7 @@ def is_dirty(self):
     @_locked
     def start(self):
         self._remove_incomplete_files()
-        if self.is_dirty():  # implies self.save_on_stop
+        if self.is_dirty():
             return self
         if self.snap_on_start:
             # pylint: disable=protected-access