uboot: Remove package
This package delivers our own U-Boot port to MT7621. Remove it, because we drop support for the ramips target. In the meantime, U-Boot upstream also has full upstream support, but given that support for the ramips target with the MT7621 subtarget and EX400 device is dropped anyways, there is no point in migrating to that.
Signed-off-by: Andreas Gnau andreas.gnau@iopsys.eu