runner can't be assigned to more than 1 group

therefore we don't need the api check.

lib/api/runners.rb

@@ -199,7 +199,6 @@ module API
 
         forbidden!("Runner is shared") if runner.is_shared?
         forbidden!("Runner associated with more than one project") if runner.projects.count > 1
-        forbidden!("Runner associated with more that one group") if runner.groups.count > 1
         forbidden!("No access granted") unless user_can_access_runner?(runner)
       end
 

spec/requests/api/runners_spec.rb

@@ -29,8 +29,6 @@ describe API::Runners do
 
   let!(:group_runner) { create(:ci_runner, description: 'Group runner', groups: [group]) }
 
-  let!(:two_groups_runner) { create(:ci_runner, description: 'Two groups runner', groups: [group, group2]) }
-
   before do
     # Set project access for users
     create(:project_member, :master, user: user, project: project)
@@ -49,7 +47,7 @@ describe API::Runners do
         expect(response).to include_pagination_headers
         expect(json_response).to be_an Array
         expect(descriptions).to contain_exactly(
-          'Project runner', 'Group runner', 'Two projects runner', 'Two groups runner'
+          'Project runner', 'Group runner', 'Two projects runner'
         )
         expect(shared).to be_falsey
       end
@@ -422,11 +420,6 @@ describe API::Runners do
           end.to change { Ci::Runner.specific.count }.by(-1)
         end
 
-        it 'does not delete group runner with more than one associated group' do
-          delete api("/runners/#{two_groups_runner.id}", user)
-          expect(response).to have_http_status(403)
-        end
-
         it 'deletes group runner for one owned group' do
           expect do
             delete api("/runners/#{group_runner.id}", user)