cosmetic: doc: driver-model: Do not number driver lists

Everytime a dead driver is removed from the list,
we must re-number. This is a painful task.

Try
  git show e53232250 -- doc/driver-model/UDM-serial.txt
  git show 6f62f4207 -- doc/driver-model/UDM-serial.txt
  git show b9f4bc34a -- doc/driver-model/UDM-serial.txt
to see what I mean.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/doc/driver-model/UDM-stdio.txt b/doc/driver-model/UDM-stdio.txt
index c0b1c90..156627b 100644
--- a/doc/driver-model/UDM-stdio.txt
+++ b/doc/driver-model/UDM-stdio.txt
@@ -158,21 +158,21 @@
 For in-depth analysis of keyboard drivers, refer to [ UDM-keyboard.txt ].
 For in-depth analysis of video drivers, refer to [ UDM-video.txt ].
 
-  1) arch/blackfin/cpu/jtag-console.c
-  -----------------------------------
+  arch/blackfin/cpu/jtag-console.c
+  --------------------------------
   This driver is a classic STDIO driver, no problem with conversion is expected.
 
-  2) board/mpl/pati/pati.c
-  ------------------------
+  board/mpl/pati/pati.c
+  ---------------------
   This driver registers with the STDIO framework, though it uses a lot of ad-hoc
   stuff which will need to be sorted out.
 
-  3) board/netphone/phone_console.c
-  ---------------------------------
+  board/netphone/phone_console.c
+  ------------------------------
   This driver is a classic STDIO driver, no problem with conversion is expected.
 
-  4) drivers/net/netconsole.c
-  ---------------------------
+  drivers/net/netconsole.c
+  ------------------------
   This driver is a classic STDIO driver, no problem with conversion is expected.
 
 IV) Other involved files (To be removed)