tests: bluetooth: shell: remove test bluetooth.shell.cdc_acm

The default integration platform for all test cases is native_sim, but
there has never been a USB device controller available for native_sim
platform. Since legacy device support has been deprecated and all tests
and samples now use the usbd test feature tag, this test cannot be
performed on native_sim.

Remove bluetooth.shell.cdc_acm to resolve CI failures.

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