Remove some definitions which could not work; conversions from datetime

 to integer unix system time conflict on the input types.
 Leave in the conversions from integer unix system time to datetime.

contrib/unixdate/unixdate.sql

 -- unixdate
 -- Routines to convert int4 (Unix system time) to datetime
---  and int4 (delta time) to timespan
+--  and int4 (delta time in seconds) to timespan
 --
 -- Thomas Lockhart (lockhart@alumni.caltech.edu)
 -- 1997-11-25
@@ -8,7 +8,7 @@
 -- This cheats and reuses existing code in the standard package.
 -- Can not include this directly because built-in functions are optimized
 --  into a cache and the duplicate function names abstime_datetime() and
---  reltime_timespan() result in duplicate constants.
+--  reltime_timespan() would result in duplicate constants.
 --
 -- This works with Postgres v6.2 and higher.
 
@@ -32,23 +32,3 @@ CREATE FUNCTION timespan(int4)
  RETURNS timespan
  AS 'select reltime_timespan($1)' LANGUAGE 'SQL';
 
---
--- Conversions back to integer
---
-
-CREATE FUNCTION datetime_abstime(datetime)
- RETURNS int4
- AS '-' LANGUAGE 'internal';
-
-CREATE FUNCTION utime(datetime)
- RETURNS int4
- AS 'select datetime_abstime($1)' LANGUAGE 'SQL';
-
-CREATE FUNCTION timespan_reltime(timespan)
- RETURNS int4
- AS '-' LANGUAGE 'internal';
-
-CREATE FUNCTION uspan(timespan)
- RETURNS int4
- AS 'select timespan_reltime($1)' LANGUAGE 'SQL';
-