configs/beagleboardx15: remove defconfig
The beagleboardx15 boards files should be moved to
board/beagleboard directory but doing so we noticed that
beagleboardx15_defconfig was failing to build on Buildroot's
Gitlab-Ci [1] due too old BSP (uboot 2016.11 and kernel 4.9)
built with the internal toolchain.
[1] https://gitlab.com/buildroot.org/buildroot/-/jobs/
7314633702
Signed-off-by: Romain Naour <[email protected]>
Cc: Theo Debrouwere <[email protected]>
Signed-off-by: Romain Naour <[email protected]>