Remove compile-time checks for always defined WM_XXX in wxMSW

The symbols in question are present at least since XP, and most of them since
Windows 2000, so remove preprocessor checks for them, they shouldn't be needed
when any remotely current compiler/SDK.

src/msw/evtloop.cpp

@@ -328,9 +328,7 @@ void wxGUIEventLoop::DoYieldFor(long eventsToProcess)
             case WM_SYSKEYUP:
             case WM_SYSCHAR:
             case WM_SYSDEADCHAR:
-#ifdef WM_UNICHAR
             case WM_UNICHAR:
-#endif
             case WM_HOTKEY:
             case WM_IME_STARTCOMPOSITION:
             case WM_IME_ENDCOMPOSITION:
@@ -349,9 +347,7 @@ void wxGUIEventLoop::DoYieldFor(long eventsToProcess)
 
             case WM_MOUSEHOVER:
             case WM_MOUSELEAVE:
-#ifdef WM_NCMOUSELEAVE
             case WM_NCMOUSELEAVE:
-#endif
 
             case WM_CUT:
             case WM_COPY: