Fix lack of highlighting in XY view when using addLitRenderable()

The XYRenderer's addLitRenderable() was ignoring the highlight shaders,
resulting in objects not appearing highlighted when selected. XYRenderer is now
refactored so that addLitRenderable() just calls the legacy addRenderable()
method (since the lighting is unimportant anyway).

radiant/xyview/XYRenderer.h

@@ -55,19 +55,19 @@ class XYRenderer: public RenderableCollector
 
     void addRenderable(Shader& shader,
                        const OpenGLRenderable& renderable,
-                       const Matrix4& world, const LightSources* lights,
+                       const Matrix4& world, const LightSources*,
                        const IRenderEntity* entity) override
     {
         if (_state.highlightPrimitives)
         {
             if (_state.highlightAsGroupMember)
                 _selectedShaderGroup->addRenderable(renderable, world,
-                                                    lights, entity);
+                                                    nullptr, entity);
             else
-                _selectedShader->addRenderable(renderable, world, lights, entity);
+                _selectedShader->addRenderable(renderable, world, nullptr, entity);
         }
 
-        shader.addRenderable(renderable, world, lights, entity);
+        shader.addRenderable(renderable, world, nullptr, entity);
     }
 
     void addLitRenderable(Shader& shader,
@@ -76,7 +76,7 @@ class XYRenderer: public RenderableCollector
                           const LitObject& /* litObject */,
                           const IRenderEntity* entity = nullptr) override
     {
-        shader.addRenderable(renderable, localToWorld, nullptr, entity);
+        addRenderable(shader, renderable, localToWorld, nullptr, entity);
     }
 
     void render(const Matrix4& modelview, const Matrix4& projection)