tools/mrvl_uart.sh: Remove script

tools/mrvl_uart.sh: Remove script

There are two tools for sending images over UART to Marvell SoCs: kwboot
and mrvl_uart.sh. kwboot received lot of new features and improvements in
last few months. There is no need to maintain two tools in U-Boot, so
remove old mrvl_uart.sh tool.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Marcel Ziswiler <marcel@ziswiler.com>
Tested-by: Marcel Ziswiler <marcel@ziswiler.com>
Reviewed-by: Tony Dinh <mibodhi@gmail.com>