uboot-tools: do not override busybox uninstall commands

The uboot-tools.mk has a copy of BUSYBOX_UNINSTALL_TARGET_CMDS
in it, presumably due to a copy/paste error.  This definition
is overriding the (identical) definition in busybox.mk.

Also, add license info.

Signed-off-by: Danomi Manchego <danomimanchego123@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>