configs/toradex_apalis_imx6: remove defconfig, broken

This defconfig no longer builds:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/11026774072

It has been broken for at least 2 months:

  https://gitlab.com/buildroot.org/buildroot/-/jobs?name=T%3Dtoradex_apalis_imx6&kind=BUILD

It uses an outdated Linux 4.9 kernel, which no longer builds with
modern toolchains.

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

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/11026774072

Cc: Sergio Prado <sergio.prado@e-labworks.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
(cherry picked from commit 1a3bae6424)
Signed-off-by: Titouan Christophe <titouan.christophe@mind.be>

DEVELOPERS

@@ -2977,8 +2977,6 @@ F:	package/wpa_supplicant/
 F:	package/xr819-xradio/
 
 N:	Sergio Prado <sergio.prado@e-labworks.com>
-F:	board/toradex/apalis-imx6/
-F:	configs/toradex_apalis_imx6_defconfig
 F:	package/aoetools/
 F:	package/asn1c/
 F:	package/azure-iot-sdk-c/