configs/andes_ae350_45_defconfig: move to external Bootlin stable toolchain

This moves the andes_ae350_45_defconfig to the Bootlin glibc stable external toolchain
as per[1].

[1]: https://elinux.org/Buildroot:DeveloperDaysELCE2024#Rules_for_defconfigs

Signed-off-by: Leo Yu-Chi Liang <ycliang@andestech.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

configs/andes_ae350_45_defconfig

@@ -1,6 +1,7 @@
 BR2_riscv=y
 BR2_RISCV_ISA_RVC=y
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_6_0=y
+BR2_TOOLCHAIN_EXTERNAL=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_LP64D_GLIBC_STABLE=y
 BR2_GLOBAL_PATCH_DIR="board/andes/ae350/patches"
 BR2_DOWNLOAD_FORCE_CHECK_HASHES=y
 BR2_TARGET_GENERIC_GETTY_PORT="ttyS0"