Get rid of macOS 10.7 version checks, they're always true

We don't support OS X < 10.7 anyhow any more.

src/osx/core/bitmap.cpp

@@ -495,11 +495,10 @@ IconRef wxBitmapRefData::GetIconRef()
         
         switch (sz)
         {
-#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7
             case 1024:
                 dataType = kIconServices1024PixelDataARGB;
                 break;
-#endif
+
             case 512:
                 dataType = kIconServices512PixelDataARGB;
                 break;