Update server hooks documentation to current behavior

doc/administration/server_hooks.md

@@ -88,11 +88,10 @@ pattern (`*~`).
 
 The hooks are searched and executed in this order:
 
-1. `gitlab-shell/hooks` directory as known to Gitaly.
-1. `<project>.git/hooks/<hook_name>` -  executed by `git` itself, this is symlinked to `gitlab-shell/hooks/<hook_name>`.
+1. Built-in GitLab server hooks (not user-customizable).
 1. `<project>.git/custom_hooks/<hook_name>` - per-project hook (this was kept as the already existing behavior).
 1. `<project>.git/custom_hooks/<hook_name>.d/*` - per-project hooks.
-1. `<project>.git/hooks/<hook_name>.d/*` OR `<custom_hooks_dir>/<hook_name.d>/*` - global hooks: all executable files (except editor backup files).
+1. `<custom_hooks_dir>/<hook_name>.d/*` - global hooks: all executable files (except editor backup files).
 
 The hooks of the same type are executed in order and execution stops on the
 first script exiting with a non-zero value.