remove mentionings of devfs in documentation

Now that devfs is removed, there's no longer any need to document how to
do this or that with devfs.

This patch includes some improvements by Joe Perches.

Signed-off-by: Adrian Bunk <bunk@stusta.de>

Documentation/usb/usb-serial.txt

@@ -13,7 +13,6 @@ CONFIGURATION
   Currently the driver can handle up to 256 different serial interfaces at
   one time. 
 
-  If you are not using devfs:
     The major number that the driver uses is 188 so to use the driver,
     create the following nodes:
 	mknod /dev/ttyUSB0 c 188 0
@@ -26,10 +25,6 @@ CONFIGURATION
 	mknod /dev/ttyUSB254 c 188 254
 	mknod /dev/ttyUSB255 c 188 255
 
-  If you are using devfs:
-    The devices supported by this driver will show up as
-    /dev/usb/tts/{0,1,...}
-
   When the device is connected and recognized by the driver, the driver
   will print to the system log, which node(s) the device has been bound
   to.