boards: use board common CDC ACM UART configuration

Remove all USB and CDC ACM configuration in favor of common
configuraiton.

Do not adapt board-specific configurations such as unknown PID/VID or
string descriptors. There is no justification for using them on specific
boards, and we do not have formal approval to use them in the project
tree. Also, we need more uniform configuration, since the main reason
for enabling CDC ACM here is to allow users to run examples like
hello_world right out of the box. Of course, anyone is free to customize
these settings in their fork or downstream project.

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