configs: remove SDL2 dependency in tools-only_defconfig

When building tools only there is no point in requiring the SDL2 library.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/configs/tools-only_defconfig b/configs/tools-only_defconfig
index 2197063..3ad9083 100644
--- a/configs/tools-only_defconfig
+++ b/configs/tools-only_defconfig
@@ -3,6 +3,7 @@
 CONFIG_ENV_SIZE=0x2000
 CONFIG_DEFAULT_DEVICE_TREE="sandbox"
 CONFIG_SYS_LOAD_ADDR=0x0
+# CONFIG_SANDBOX_SDL is not set
 CONFIG_ANDROID_BOOT_IMAGE=y
 CONFIG_FIT=y
 CONFIG_TIMESTAMP=y