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 <romain.naour@smile.fr>
Cc: Theo Debrouwere <t.debrouwere@televic.com>
Signed-off-by: Romain Naour <romain.naour@smile.fr>

.checkpackageignore

@@ -142,7 +142,6 @@ configs/bananapi_m2_berry_defconfig lib_defconfig.ForceCheckHash
 configs/bananapi_m2_ultra_defconfig lib_defconfig.ForceCheckHash
 configs/bananapi_m2_zero_defconfig lib_defconfig.ForceCheckHash
 configs/bananapro_defconfig lib_defconfig.ForceCheckHash
-configs/beagleboardx15_defconfig lib_defconfig.ForceCheckHash
 configs/beaglebone_defconfig lib_defconfig.ForceCheckHash
 configs/beaglev_defconfig lib_defconfig.ForceCheckHash
 configs/beelink_gs1_defconfig lib_defconfig.ForceCheckHash

DEVELOPERS

@@ -3029,8 +3029,6 @@ N:	Tan En De <ende.tan@starfivetech.com>
 F:	package/libkcapi/
 
 N:	Theo Debrouwere <t.debrouwere@televic.com>
-F:	board/beagleboardx15/
-F:	configs/beagleboardx15_defconfig
 F:	package/pugixml/
 
 N:	Thierry Bultel <tbultel@free.fr>

board/beagleboardx15/genimage.cfg

@@ -1,27 +0,0 @@
-image boot.vfat {
-	vfat {
-		files = {
-			"MLO",
-			"u-boot.img"
-		}
-	}
-
-	size = 4M
-}
-
-image sdcard.img {
-	hdimage {
-	}
-
-	partition u-boot {
-		partition-type = 0xC
-		bootable = "true"
-		image = "boot.vfat"
-	}
-
-	partition rootfs {
-		partition-type = 0x83
-		image = "rootfs.ext4"
-		size = 512M
-	}
-}

board/beagleboardx15/readme.txt

@@ -1,49 +0,0 @@
-BeagleBoard X15
-
-Intro
-=====
-This config currently supports the beagleboard x15,
-and generates a barebone image.
-
-The image must be flashed to a SD card to be used.
-
-How to build it
-===============
-
-  $ make beagleboardx15_defconfig
-
-Then you can edit the build options using
-
-  $ make menuconfig
-
-Compile all and build a sdcard image:
-
-  $ make
-
-Result of the build
--------------------
-
-After building, you should get a tree like this:
-
-  output/images/
-  +-- am57xx-beagle-x15.dtb
-  +-- am57xx-beagle-x15-revb1.dtb
-  +-- boot.vfat
-  +-- MLO
-  +--rootfs.ext2
-  +-- rootfs.ext4
-  +-- rootfs.tar
-  +-- sdcard.img
-  +-- u-boot.img
-  +-- u-boot-spl.bin
-  +-- zImage
-
-How to write the microSD card
-=============================
-
-Once the build process is finished you will have an image called "sdcard.img"
-in the output/images/ directory.
-
-Copy the bootable "sdcard.img" onto an SD card with "dd":
-
-  $ sudo dd if=output/images/sdcard.img of=/dev/sdX

configs/beagleboardx15_defconfig

@@ -1,29 +0,0 @@
-BR2_arm=y
-BR2_cortex_a15=y
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_4_9=y
-BR2_ROOTFS_POST_IMAGE_SCRIPT="support/scripts/genimage.sh"
-BR2_ROOTFS_POST_SCRIPT_ARGS="-c board/beagleboardx15/genimage.cfg"
-BR2_LINUX_KERNEL=y
-BR2_LINUX_KERNEL_CUSTOM_VERSION=y
-BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.9"
-BR2_LINUX_KERNEL_DEFCONFIG="omap2plus"
-BR2_LINUX_KERNEL_DTS_SUPPORT=y
-BR2_LINUX_KERNEL_INTREE_DTS_NAME="am57xx-beagle-x15 am57xx-beagle-x15-revb1"
-BR2_LINUX_KERNEL_INSTALL_TARGET=y
-BR2_TARGET_ROOTFS_EXT2=y
-BR2_TARGET_ROOTFS_EXT2_4=y
-BR2_TARGET_UBOOT=y
-BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
-BR2_TARGET_UBOOT_CUSTOM_VERSION=y
-BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2016.11"
-BR2_TARGET_UBOOT_BOARD_DEFCONFIG="am57xx_evm"
-BR2_TARGET_UBOOT_NEEDS_DTC=y
-# BR2_TARGET_UBOOT_FORMAT_BIN is not set
-BR2_TARGET_UBOOT_FORMAT_IMG=y
-BR2_TARGET_UBOOT_FORMAT_CUSTOM=y
-BR2_TARGET_UBOOT_FORMAT_CUSTOM_NAME="spl/u-boot-spl.bin"
-BR2_TARGET_UBOOT_SPL=y
-BR2_TARGET_UBOOT_SPL_NAME="MLO"
-BR2_PACKAGE_HOST_DOSFSTOOLS=y
-BR2_PACKAGE_HOST_GENIMAGE=y
-BR2_PACKAGE_HOST_MTOOLS=y