MAINTAINERS: Remove duplicate entry for usbip driver

The usbip driver was moved out of staging in 3.17-rc3 but the MAINTAINERS file
still has the old staging entry as well as the new one. Remove the old entry.

Signed-off-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>