storage/reflink: start(): no need to go through size() getter

stop() updates the _size of a volatile volume. And after a crash,
88fa6b4 ("qubesd: at startup, stop storage for stopped qubes") takes
care of running stop() before the next start().

qubes/storage/reflink.py

@@ -214,10 +214,7 @@ def start(self):  # pylint: disable=invalid-overridden-method
             if self.snap_on_start or self.save_on_stop:
                 _copy_file(self._path_clean, self._path_dirty)
             else:
-                # Preferably use the size of a leftover image, in case
-                # the volume was previously resized - but then a crash
-                # prevented qubes.xml serialization of the new size.
-                _create_sparse_file(self._path_dirty, self.size)
+                _create_sparse_file(self._path_dirty, self._size)
         return self
 
     @qubes.storage.Volume.locked