usb: otg: kill langwell_otg driver

The way this driver was added by f0ae849d (usb: Add Intel Langwell USB
OTG Transceiver Driver) never even compiled together with langwell_udc,
and that's the only way for it to be useful.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: stable@vger.kernel.org # v2.6.31+
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Alan Cox <alan@linux.intel.com>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Felipe Balbi <balbi@ti.com>