GitLab: update Gitolite service description

wiki/src/contribute/working_together/roles/sysadmins.mdwn

@@ -242,8 +242,8 @@ Below, importance level is evaluated based on:
 
 * purpose:
   - host Git repositories used by the puppetmaster and other services
-  - host the Tails [[main repository|contribute/git#main-repo]]
-    and our website's underlays
+  - host mirrors of various Git repositories needed on lizard,
+    and whose canonical copy lives on GitLab
 * access: Tails core developers only
 * tools: [[!debpts gitolite3]]
 * configuration: `tails::gitolite` class in [[!tails_gitweb_repo