glx: remove unused __glXPreferEGL() declaration

The function definition is no longer around, drop the useless declaration.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glx/glxclient.h

@@ -646,8 +646,6 @@ extern void __glXSendLargeCommand(struct glx_context *, const GLvoid *, GLint,
 /* Initialize the GLX extension for dpy */
 extern struct glx_display *__glXInitialize(Display *);
 
-extern void __glXPreferEGL(int state);
-
 /************************************************************************/
 
 extern int __glXDebug;