On second thought, we'd better just drop these tests altogether.

Further experimentation reveals that my previous change didn't fix the
issue entirely: these tests would still fail at the spring-forward DST
transition.  There doesn't seem to be any great value in testing this
specific issue for both timestamp and timestamptz, so just lose the
latter tests.

src/test/regress/expected/horology.out

@@ -639,54 +639,12 @@ SELECT (timestamp with time zone 'today' = (timestamp with time zone 'tomorrow'
  t
 (1 row)
 
-SELECT (timestamp with time zone 'today 10:30-08' = timestamptz(date 'today', time with time zone '10:30 -08')) as "True";
- True 
-------
- t
-(1 row)
-
-SELECT (timestamp with time zone '10:30-08 today' = timestamptz(date 'today', time with time zone '10:30 -08')) as "True";
- True 
-------
- t
-(1 row)
-
 SELECT (timestamp with time zone 'tomorrow' = (timestamp with time zone 'yesterday' + interval '2 days')) as "True";
  True 
 ------
  t
 (1 row)
 
-SELECT (timestamp with time zone 'tomorrow 10:30-08' = (timestamp with time zone 'today 10:30-08' + interval '1 day')) as "True";
- True 
-------
- t
-(1 row)
-
-SELECT (timestamp with time zone '10:30-08 tomorrow' = (timestamp with time zone 'today 10:30-08' + interval '1 day')) as "True";
- True 
-------
- t
-(1 row)
-
-SELECT (timestamp with time zone 'yesterday 12:34:56-7' = timestamptz(date 'yesterday', time with time zone '12:34:56-7')) as "True";
- True 
-------
- t
-(1 row)
-
-SELECT (timestamp with time zone '12:34:56 yesterday -7' = timestamptz(date 'yesterday', time with time zone '12:34:56-7')) as "True";
- True 
-------
- t
-(1 row)
-
-SELECT (timestamp with time zone '12:34:56-7 yesterday' = timestamptz(date 'yesterday', time with time zone '12:34:56-7')) as "True";
- True 
-------
- t
-(1 row)
-
 SELECT (timestamp with time zone 'tomorrow' > 'now') as "True";
  True 
 ------

src/test/regress/sql/horology.sql

@@ -118,14 +118,7 @@ SELECT timestamp with time zone '1999-12-01' + interval '1 month - 1 second' AS
 
 SELECT (timestamp with time zone 'today' = (timestamp with time zone 'yesterday' + interval '1 day')) as "True";
 SELECT (timestamp with time zone 'today' = (timestamp with time zone 'tomorrow' - interval '1 day')) as "True";
-SELECT (timestamp with time zone 'today 10:30-08' = timestamptz(date 'today', time with time zone '10:30 -08')) as "True";
-SELECT (timestamp with time zone '10:30-08 today' = timestamptz(date 'today', time with time zone '10:30 -08')) as "True";
 SELECT (timestamp with time zone 'tomorrow' = (timestamp with time zone 'yesterday' + interval '2 days')) as "True";
-SELECT (timestamp with time zone 'tomorrow 10:30-08' = (timestamp with time zone 'today 10:30-08' + interval '1 day')) as "True";
-SELECT (timestamp with time zone '10:30-08 tomorrow' = (timestamp with time zone 'today 10:30-08' + interval '1 day')) as "True";
-SELECT (timestamp with time zone 'yesterday 12:34:56-7' = timestamptz(date 'yesterday', time with time zone '12:34:56-7')) as "True";
-SELECT (timestamp with time zone '12:34:56 yesterday -7' = timestamptz(date 'yesterday', time with time zone '12:34:56-7')) as "True";
-SELECT (timestamp with time zone '12:34:56-7 yesterday' = timestamptz(date 'yesterday', time with time zone '12:34:56-7')) as "True";
 SELECT (timestamp with time zone 'tomorrow' > 'now') as "True";
 
 -- timestamp with time zone, interval arithmetic around DST change