Revert "p2v: Add usb-storage dracut module to allow boot from USB key (RHBZ#1157679)."

Running 'dracut -f' installs a dracut for the running kernel (of the
appliance) not the installed kernel.  Stupid stupid stupid.

This reverts commit 7a6d44ebfe23f28f46f6af1fd48ea8371473529b.