x11: Don't include X11/extensions/extutil.h

We don't use it, it was a leftover from 1.2, I think, and it doesn't exist
on Solaris, so this should hopefully fix the build there.

This also means we don't need the configure/cmake checks for
SDL_VIDEO_DRIVER_X11_CONST_PARAM_XEXTADDDISPLAY, so that was removed also.

Fixes #1666.

include/SDL_config.h.cmake

@@ -422,7 +422,6 @@
 #cmakedefine SDL_VIDEO_DRIVER_X11_XSHAPE @SDL_VIDEO_DRIVER_X11_XSHAPE@
 #cmakedefine SDL_VIDEO_DRIVER_X11_XVIDMODE @SDL_VIDEO_DRIVER_X11_XVIDMODE@
 #cmakedefine SDL_VIDEO_DRIVER_X11_SUPPORTS_GENERIC_EVENTS @SDL_VIDEO_DRIVER_X11_SUPPORTS_GENERIC_EVENTS@
-#cmakedefine SDL_VIDEO_DRIVER_X11_CONST_PARAM_XEXTADDDISPLAY @SDL_VIDEO_DRIVER_X11_CONST_PARAM_XEXTADDDISPLAY@
 #cmakedefine SDL_VIDEO_DRIVER_X11_HAS_XKBKEYCODETOKEYSYM @SDL_VIDEO_DRIVER_X11_HAS_XKBKEYCODETOKEYSYM@
 #cmakedefine SDL_VIDEO_DRIVER_VITA @SDL_VIDEO_DRIVER_VITA@
 

include/SDL_config.h.in

@@ -395,7 +395,6 @@
 #undef SDL_VIDEO_DRIVER_X11_XSHAPE
 #undef SDL_VIDEO_DRIVER_X11_XVIDMODE
 #undef SDL_VIDEO_DRIVER_X11_SUPPORTS_GENERIC_EVENTS
-#undef SDL_VIDEO_DRIVER_X11_CONST_PARAM_XEXTADDDISPLAY
 #undef SDL_VIDEO_DRIVER_X11_HAS_XKBKEYCODETOKEYSYM
 #undef SDL_VIDEO_DRIVER_NACL
 #undef SDL_VIDEO_DRIVER_VIVANTE

include/SDL_config_macosx.h

@@ -202,7 +202,6 @@
  */
 #define SDL_VIDEO_DRIVER_X11_XINPUT2 1
 #define SDL_VIDEO_DRIVER_X11_SUPPORTS_GENERIC_EVENTS 1
-#define SDL_VIDEO_DRIVER_X11_CONST_PARAM_XEXTADDDISPLAY 1
 #endif
 
 #ifndef SDL_VIDEO_RENDER_OGL