configure: nuke --with-max-{width,height}

Unused as of commit 630ab0d27ba(mesa: remove last of MAX_WIDTH,
MAX_HEIGHT). Update all the remaining references to the defines.

v2: Use the correct variable name in the comments

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

include/GL/osmesa.h

@@ -41,10 +41,8 @@
  *   OSMesaGetIntegerv - return OSMesa state parameters
  *
  *
- * The limits on the width and height of an image buffer are MAX_WIDTH and
- * MAX_HEIGHT as defined in Mesa/src/config.h.  Defaults are 1280 and 1024.
- * You can increase them as needed but beware that many temporary arrays in
- * Mesa are dimensioned by MAX_WIDTH or MAX_HEIGHT.
+ * The limits on the width and height of an image buffer can be retrieved
+ * via OSMesaGetIntegerv(OSMESA_MAX_WIDTH/OSMESA_MAX_HEIGHT).
  */