[NET]: Remove Documentation/networking/pt.txt

There's no no point in keeping documentation for a driver that was
removed many years ago.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/00-INDEX

@@ -80,8 +80,6 @@ olympic.txt
 	- IBM PCI Pit/Pit-Phy/Olympic Token Ring driver info.
 policy-routing.txt
 	- IP policy-based routing
-pt.txt
-	- the Gracilis Packetwin AX.25 device driver
 ray_cs.txt
 	- Raylink Wireless LAN card driver info.
 shaper.txt