Revert "Add a background brush to the window"

While this does get rid of artifacts, it can also add a brief moment
where the gray background becomes visible when the window reconfigures
which can look jarring.

This reverts commit 35c7138333.

src/wine-host/editor.cpp

@@ -682,7 +682,6 @@ ATOM register_window_class(std::string window_class_name) {
     window_class.lpfnWndProc = window_proc;
     window_class.hInstance = GetModuleHandle(nullptr);
     window_class.hCursor = LoadCursor(nullptr, IDC_ARROW);
-    window_class.hbrBackground = CreateSolidBrush(RGB(32, 32, 32));
     window_class.lpszClassName = window_class_name.c_str();
 
     return RegisterClassEx(&window_class);