usb: usb-mx2: Remove unused file

i.MX21 support has been dropped, so remove such unused file.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20210304023220.2362407-1-festevam@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>