[SERIAL] feature-removal-schedule.txt: remove {,un}register_serial entry

If the feature is removed, there's no need to keep the entry in
feature-removal-schedule.txt.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

Documentation/feature-removal-schedule.txt

@@ -102,16 +102,6 @@ Who:	Jody McIntyre <scjody@steamballoon.com>
 
 ---------------------------
 
-What:	register_serial/unregister_serial
-When:	September 2005
-Why:	This interface does not allow serial ports to be registered against
-	a struct device, and as such does not allow correct power management
-	of such ports.  8250-based ports should use serial8250_register_port
-	and serial8250_unregister_port, or platform devices instead.
-Who:	Russell King <rmk@arm.linux.org.uk>
-
----------------------------
-
 What:	i2c sysfs name change: in1_ref, vid deprecated in favour of cpu0_vid
 When:	November 2005
 Files:	drivers/i2c/chips/adm1025.c, drivers/i2c/chips/adm1026.c