samples: disable CDC ACM logging

Disable CDC ACM logging in the configuration overlays used to select the
CDC ACM UART as the shell backend.
The build warning was introduced by the commit e8c48678
("usb: cdc_acm: disable logging if used for shell with logging")
to prevent recursive logging when using the CDC ACM UART as shell or
logging backend

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>