samples: video: capture: remove stray USB legacy stack configuration

The legacy USB device stack configuration used in the board
configuration overlay files has been deprecated. It is not causing CI
failures because the board lacks a test feature 'video' and is filtered
out in CI.

Besides the deprecated configuration, the sample code does not enable
the USB device stack, so it is not used anyway. Even if it were needed,
the correct way to enable logging via USB CDC ACM would be to use the
cdc-acm-console snippet.

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