configs: remove calao_snowball_defconfig

This defconfig has not been updated since a long time, and it now
fails to build because the latest version of U-Boot has removed for
the Snowball because nobody converted it to the new U-Boot
standards. And our defconfig was not specifying an explicit U-Boot
version for it.

On the kernel side, the Git repository has not seen any commits since
3 years, and generally speaking, the Snowball project and the SoC it
is based on are no longer being developed.

Consequently, let's get rid of this defconfig altogether.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

configs/calao_snowball_defconfig

@@ -1,23 +0,0 @@
-BR2_arm=y
-BR2_cortex_a9=y
-BR2_KERNEL_HEADERS_3_4=y
-BR2_ARM_FPU_VFPV3D16=y
-BR2_TOOLCHAIN_BUILDROOT_WCHAR=y
-BR2_TOOLCHAIN_BUILDROOT_CXX=y
-BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
-BR2_TARGET_GENERIC_GETTY_PORT="ttyAMA2"
-BR2_PACKAGE_BUSYBOX_SHOW_OTHERS=y
-BR2_PACKAGE_SNOWBALL_HDMISERVICE=y
-BR2_PACKAGE_LIBNL=y
-BR2_PACKAGE_SNOWBALL_INIT=y
-BR2_PACKAGE_WPA_SUPPLICANT=y
-BR2_TARGET_ROOTFS_TAR_GZIP=y
-BR2_TARGET_UBOOT=y
-BR2_TARGET_UBOOT_BOARDNAME="snowball"
-BR2_LINUX_KERNEL=y
-BR2_LINUX_KERNEL_CUSTOM_GIT=y
-BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/igloocommunity/igloo-kernel"
-BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="stable-linux-ux500-3.4"
-BR2_LINUX_KERNEL_PATCH="board/calao/snowball/"
-BR2_LINUX_KERNEL_DEFCONFIG="u8500"
-BR2_LINUX_KERNEL_INSTALL_TARGET=y