staging: sep: remove driver

Looks like no one's working on the driver anymore, so remove it for now.
If someone wants to work on moving it out of staging, this commit can be
reverted.

Signed-off-by: Kristina Martšenko <kristina.martsenko@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Mark A. Allyn <mark.a.allyn@intel.com>
Cc: Jayant Mangalampalli <jayant.mangalampalli@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>