cosmetic: UDM-net: clean up the remainders of dead driver

This commit omits non-existing drivers/net/netarm_eth.c from the list.
This driver is deleted by commit b411eb30f.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

doc/driver-model/UDM-net.txt

@@ -338,12 +338,6 @@ III) Analysis of in-tree drivers
   This file implements external functions necessary for native NE2000 compatible
   networking card to work.
 
-  drivers/net/netarm_eth.c
-  ------------------------
-
-  This driver uses the old, legacy, network API and will either have to be
-  converted or removed.
-
   drivers/net/netconsole.c
   ------------------------