Move EE code out of API::Services

This moves EE specific code out of API::Services and into
EE::API::Services.

ee/lib/ee/api/services.rb

+# frozen_string_literal: true
+
+module EE
+  module API
+    module Services
+      extend ActiveSupport::Concern
+
+      prepended do
+        desc "Trigger a global slack command" do
+          detail 'Added in GitLab 9.4'
+        end
+        post 'slack/trigger' do
+          if result = SlashCommands::GlobalSlackHandler.new(params).trigger
+            status result[:status] || 200
+            present result
+          else
+            not_found!
+          end
+        end
+      end
+    end
+  end
+end

lib/api/services.rb

@@ -160,17 +160,7 @@ module API
         end
       end
     end
-
-    desc "Trigger a global slack command" do
-      detail 'Added in GitLab 9.4'
-    end
-    post 'slack/trigger' do
-      if result = SlashCommands::GlobalSlackHandler.new(params).trigger
-        status result[:status] || 200
-        present result
-      else
-        not_found!
-      end
-    end
   end
 end
+
+API::Services.prepend(EE::API::Services)