fix task message validator

Author: oliver-sanders

src/user-guide/task-implementation/job-scripts.rst

@@ -182,8 +182,7 @@ status message does not get through, the server will recover the correct task
 status by polling on job timeout (or earlier if regular polling is
 configured).
 
-Task messages are validated by
-:py:class:`cylc.flow.unicode_rules.TaskMessageValidator`.
+Task messages are validated by:
 
 .. autoclass:: cylc.flow.unicode_rules.TaskMessageValidator
    :noindex: