CI: Mitigate one occurrence of py/unused-local-variable

Author: amotl

src/crate/testing/layer.py

@@ -358,7 +358,6 @@ def _wait_for(self, validator):
                 time.sleep(self.wait_interval)
 
         self.monitor.consumers.remove(line_buf)
-        line_buf = None
 
     def _wait_for_start(self):
         """Wait for instance to be started"""