Fix regression in Git Annex permission check

The `changes` in git-annex-shell mean a different thing than
git-receive-pack. Revert to the previous code and use a simple check
whether Git Annex is enabled.

CHANGELOG-EE

@@ -4,6 +4,7 @@ v 8.11.0 (unreleased)
   - Performance improvement of push rules
 
 v 8.10.3 (unreleased)
+  - Fix regression in Git Annex permission check
 
 v 8.10.2
   - Fix pagination on search result page when ES search is enabled. !592

lib/gitlab/git_access.rb

@@ -253,6 +253,8 @@ module Gitlab
     end
 
     def git_annex_access_check(project, changes)
+      return false unless Gitlab.config.gitlab_shell.git_annex_enabled
+
       unless user && user_access.allowed?
         return build_status_object(false, "You don't have access")
       end
@@ -265,7 +267,7 @@ module Gitlab
         return build_status_object(false, "You can't use git-annex with a secondary GitLab Geo node.")
       end
 
-      if user.can?(:push_code, project) && git_annex_branch_sync?(changes)
+      if user.can?(:push_code, project)
         build_status_object(true)
       else
         build_status_object(false, "You don't have permission")