don't filter group runners by project flag

the scope `Ci::Runner.belonging_to_group` does not filter out the
runners where the projects has `#group_runners_enabled` set to false
anymore.

it didn't show up in the runners UI anymore when group runners were
disabled. this was confusing.

the flag is only relevant when selecting appropriate runner for a build.

app/models/ci/runner.rb

@@ -37,15 +37,7 @@ module Ci
           INNER JOIN namespaces ON namespaces.id = ci_runner_groups.group_id
           INNER JOIN projects ON projects.namespace_id = namespaces.id
         }
-      ).where(
-        %{
-          projects.id = :project_id
-            AND
-          projects.group_runners_enabled = :true
-        },
-          project_id: project_id,
-          true: true
-      )
+      ).where('projects.id = :project_id', project_id: project_id)
     }
 
     scope :owned_or_shared, -> (project_id) do

spec/models/ci/runner_spec.rb

@@ -93,14 +93,6 @@ describe Ci::Runner do
 
       expect(described_class.belonging_to_group(specific_project.id)).to eq [specific_runner]
     end
-
-    it 'does not return the group runner if the project has group runners disabled' do
-      specific_group = create :group
-      specific_project = create :project, group: specific_group, group_runners_enabled: false
-      create :ci_runner, :specific, groups: [specific_group]
-
-      expect(described_class.belonging_to_group(specific_project.id)).to be_empty
-    end
   end
 
   describe '.owned_or_shared' do