tests/usbus_cdc_ecm: remove Kconfig file
tests/usbus_cdc_ecm: remove Kconfig file

This is not longer needed since 250f6fdfa341ffcf0534b8adbec436d0bf4e3a57
moved the default PID and VID values to the System USB Kconfig.

OlegHahm/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,miri64/RIOT,jasonatran/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,jasonatran/RIOT,jasonatran/RIOT,kYc0o/RIOT,miri64/RIOT,jasonatran/RIOT,ant9000/RIOT,authmillenon/RIOT,kaspar030/RIOT,kaspar030/RIOT,OlegHahm/RIOT,kaspar030/RIOT,OTAkeys/RIOT,miri64/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,miri64/RIOT,miri64/RIOT,OTAkeys/RIOT,kYc0o/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,authmillenon/RIOT,OTAkeys/RIOT,ant9000/RIOT,ant9000/RIOT,ant9000/RIOT,jasonatran/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,ant9000/RIOT,kYc0o/RIOT,authmillenon/RIOT,kYc0o/RIOT