ui/gl: GLContext: access directly class member

In ::EndSwap, dc_ class member was accessed through a function. Access
it directly like it is done elsewhere in the class.

It is also the only place where it is used, so remove the function in
question.

src/xenia/ui/gl/gl_context.cc

@@ -463,7 +463,7 @@ void GLContext::BeginSwap() {
 
 void GLContext::EndSwap() {
   SCOPE_profile_cpu_i("gpu", "xe::ui::gl::GLContext::EndSwap");
-  SwapBuffers(dc());
+  SwapBuffers(dc_);
 }
 
 }  // namespace gl

src/xenia/ui/gl/gl_context.h

@@ -35,8 +35,6 @@ class GLContext : public GraphicsContext {
  public:
   ~GLContext() override;
 
-  HDC dc() const { return dc_; }
-
   ImmediateDrawer* immediate_drawer() override;
 
   bool is_current() override;