Move defaultDisplayClass to xdmcp-only visibility.

dix/globals.c

@@ -136,7 +136,6 @@ Bool screenSaverSuspended = FALSE;
 char *defaultFontPath = COMPILEDDEFAULTFONTPATH;
 char *defaultTextFont = COMPILEDDEFAULTFONT;
 char *defaultCursorFont = COMPILEDCURSORFONT;
-char *defaultDisplayClass = COMPILEDDISPLAYCLASS;
 FontPtr defaultFont;   /* not declared in dix.h to avoid including font.h in
 			every compilation of dix code */
 CursorPtr rootCursor;