Docs - remove mention of --max-exit-timeout from heterogeneous_jobs.shtml.

Otherwise undocumented, and does not do anything.
Will be removed in 18.08.

doc/html/heterogeneous_jobs.shtml

@@ -69,7 +69,6 @@ A list of propagated options follows.</p>
 <li>--job-name</li>
 <li>--kill-on-bad-exit  (option available only in srun)</li>
 <li>--label             (option available only in srun)</li>
-<li>--max-exit-timeout  (option available only in srun)</li>
 <li>--mcs-label</li>
 <li>--msg-timeout       (option available only in srun)</li>
 <li>--no-allocate       (option available only in srun)</li>