Clear plugin repository when stopping tuning

Not clearing it before a profile switch would
result in never deleting the original plugin
objects - those would accumulate in memory with
each profile switch.

Relates: RHEL-36442

tuned/units/manager.py

@@ -135,7 +135,7 @@ def destroy_all(self):
 		for plugin in self._plugins:
 			log.debug("cleaning plugin '%s'" % plugin.name)
 			self._try_call("destroy_all", None, plugin.cleanup)
-
+		self._plugins_repository.plugins.clear()
 		del self._plugins[:]
 		del self._instances[:]