Remove debugging strdup()

This was not meant to be included in the previous commit. The static
storage for the font string is more than enough.

vncviewer/fltk/theme.cxx

       CFStringGetCString(name, font_name, sizeof(font_name),
                          kCFStringEncodingUTF8);
 
-      Fl::set_font(FL_HELVETICA, strdup(font_name));
+      Fl::set_font(FL_HELVETICA, font_name);
 
       CFRelease(name);
     }