features.csv fix Delete Group API docs link

and for now leave latest Synapse version in link description. TBD how to handle
deprecated/removed API's.

doc/source/features.csv

@@ -1,7 +1,7 @@
 Synapse Admin API,synadm command group / synadm command
 `Acount Validity APIs Overview <https://element-hq.github.io/synapse/develop/admin_api/account_validity.html>`_,
 - `Renew account <https://element-hq.github.io/synapse/develop/admin_api/account_validity.html#renew-account>`_,
-"`Delete Group API [dead, API gone?] <https://element-hq.github.io/synapse/develop/admin_api/delete_group.html>`_",- :doc:`synadm.cli.group`
+`Delete Group API [Synapse 1.6.1] <https://element-hq.github.io/synapse/v1.61/admin_api/delete_group.html>`_,- :doc:`synadm.cli.group`
 `Background Update APIs Overview <https://element-hq.github.io/synapse/develop/usage/administration/admin_api/background_updates.html>`_,
 - `Event Reports APIs Overview <https://element-hq.github.io/synapse/develop/admin_api/event_reports.html>`_,
 - `Show reported events <https://element-hq.github.io/synapse/develop/admin_api/event_reports.html#show-reported-events>`_,