Move McMurdo and South Pole to 'backward'.

This continues in the series of moving entries to 'backward' if
they exist only because of obsolete tz rules about country codes.
This change does not affect any time stamps after 1970.  Unlike
the previous change in this series, this one does affect time
stamps before 1970, but that's OK as pre-1970 time stamps are
out of scope for the tz database.
* antarctica (Antarctica/McMurdo, Antarctica/South_Pole):
Move to 'backward' and link to Pacific/Auckland.
* backward: Move links here from 'antarctica'.
* zone.tab: Coalesce McMurdo and South Pole, and add Scott Base
to the description.

antarctica

@@ -228,7 +228,8 @@ Zone Antarctica/Syowa	0	-	zzz	1957 Jan 29
 # Scott Island (never inhabited)
 #
 # year-round base
-# Scott, Ross Island, since 1957-01, is like Antarctica/McMurdo.
+# Scott Base, Ross Island, since 1957-01.
+# See Pacific/Auckland.
 #
 # These rules for New Zealand are stolen from the `australasia' file.
 # Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
@@ -337,16 +338,11 @@ Zone Antarctica/Palmer	0	-	zzz	1965
 			-4:00	ChileAQ	CL%sT
 #
 #
-# McMurdo, Ross Island, since 1955-12
-# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone Antarctica/McMurdo	0	-	zzz	1956
-			12:00	NZAQ	NZ%sT
+# McMurdo Station, Ross Island, since 1955-12
+# See Pacific/Auckland.
 #
-# Amundsen-Scott, South Pole, continuously occupied since 1956-11-20
-#
-# From Paul Eggert (1996-09-03):
-# Normally it wouldn't have a separate entry, since it's like the
-# larger Antarctica/McMurdo since 1970, but it's too famous to omit.
+# Amundsen-Scott South Pole Station, continuously occupied since 1956-11-20
+# See Pacific/Auckland.
 #
 # From Chris Carrier (1996-06-27):
 # Siple, the first commander of the South Pole station,
@@ -367,5 +363,3 @@ Zone Antarctica/McMurdo	0	-	zzz	1956
 # makes all of the clocks run fast.  So every couple of days,
 # we have to go around and set them back 5 minutes or so.
 # Maybe if we let them run fast all of the time, we'd get to leave here sooner!!
-#
-Link	Antarctica/McMurdo	Antarctica/South_Pole