Define yabridge Window class name in header

Apparently this is used in xdnd-proxy.cpp.

src/wine-host/editor.cpp

@@ -41,12 +41,6 @@ using namespace std::literals::string_literals;
         }                                                               \
     } while (0)
 
-/**
- * The name of the Win32 window class we'll use for the Win32 window that the
- * plugin can embed itself in.
- */
-constexpr char yabridge_window_class_name[] = "yabridge plugin";
-
 /**
  * The Win32 timer ID we'll use to periodically call the VST2 `effeditidle`
  * function with. We have to do this on a timer because the function has to be