Remove /reassign quick action

/reassign should only work when multiple assignees are available. And
since this is only the case for GitLab EE, remove it from CE.

This was picked using 517c97eb of gitlab-ee.

app/services/quick_actions/interpret_service.rb

@@ -146,32 +146,6 @@ module QuickActions
         end
     end
 
-    desc do
-      "Change assignee#{'(s)' if issuable.allows_multiple_assignees?}"
-    end
-    explanation do |users|
-      users = issuable.allows_multiple_assignees? ? users : users.take(1)
-      "Change #{'assignee'.pluralize(users.size)} to #{users.map(&:to_reference).to_sentence}."
-    end
-    params do
-      issuable.allows_multiple_assignees? ? '@user1 @user2' : '@user'
-    end
-    condition do
-      issuable.persisted? &&
-        current_user.can?(:"admin_#{issuable.to_ability_name}", project)
-    end
-    parse_params do |assignee_param|
-      extract_users(assignee_param)
-    end
-    command :reassign do |users|
-      @updates[:assignee_ids] =
-        if issuable.allows_multiple_assignees?
-          users.map(&:id)
-        else
-          [users.last.id]
-        end
-    end
-
     desc 'Set milestone'
     explanation do |milestone|
       "Sets the milestone to #{milestone.to_reference}." if milestone

changelogs/unreleased/tc-follow-up-mia.yml

+---
+title: Undo adding the /reassign quick action
+merge_request: 12701
+author:

spec/services/quick_actions/interpret_service_spec.rb

@@ -431,22 +431,6 @@ describe QuickActions::InterpretService, services: true do
       end
     end
 
-    context 'reassign command' do
-      let(:content) { '/reassign' }
-
-      context 'Issue' do
-        it 'reassigns user if content contains /reassign @user' do
-          user = create(:user)
-
-          issue.update(assignee_ids: [developer.id])
-
-          _, updates = service.execute("/reassign @#{user.username}", issue)
-
-          expect(updates).to eq(assignee_ids: [user.id])
-        end
-      end
-    end
-
     it_behaves_like 'milestone command' do
       let(:content) { "/milestone %#{milestone.title}" }
       let(:issuable) { issue }