Revert "Remove a modprobe warning in new systems."

This breaks switching to the bridge networking - this change means
/etc/modprobe.d/blacklist-bridge is not deleted when switching to
bridge, which means after the host reboots it can't load the ethernet
bridging kernel module and networking is totally broken.

This reverts commit 37eee6eff0ce3fb4a0185e6f4aa03094c0668844.