configs/odroidxu4: remove defconfig, broken

This defconfig no longer builds:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/11012273936

It has been broken for over 2 months:

  https://gitlab.com/buildroot.org/buildroot/-/jobs?name=T%3Dodroidxu4&kind=BUILD

Most likely the U-Boot version used is no longer compatible with
recent toolchains.

Unless a fix is provided, this defconfig will be removed.

Cc: Pierre Crokaert <pct@crookies.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
(cherry picked from commit 585527b872)
Signed-off-by: Titouan Christophe <titouan.christophe@mind.be>

DEVELOPERS

@@ -2707,10 +2707,6 @@ F:	package/liburcu/
 N:	Philippe Reynes <philippe.reynes@softathome.com>
 F:	package/ibm-sw-tpm2/
 
-N:	Pierre Crokaert <pct@crookies.net>
-F:	board/hardkernel/odroidxu4/
-F:	configs/odroidxu4_defconfig
-
 N:	Pierre Ducroquet <pinaraf@pinaraf.info>
 F:	package/kf5/