pgsql: Remove timetravel extension.

Remove timetravel extension.

The extension depended on old types which are about to be removed. As
the code additionally was pretty crufty and didn't provide much in the
way of functionality, removing the extension seems to be the best way
forward.  It's fairly trivial to write functionality in plpgsql that
more than covers what timetravel did.

Author: Andres Freund
Discussion:
    https://postgr.es/m/20171213080506.cwjkpcz3bkk6yz2u@alap3.anarazel.de
    https://postgr.es/m/25615.1513115237@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/2d10defa7771931295ee804cf096fb9388472a7b

Modified Files
--------------
contrib/spi/Makefile                        |   7 +-
contrib/spi/timetravel--1.0.sql             |  19 -
contrib/spi/timetravel--unpackaged--1.0.sql |   8 -
contrib/spi/timetravel.c                    | 553 ----------------------------
contrib/spi/timetravel.control              |   5 -
contrib/spi/timetravel.example              |  81 ----
doc/src/sgml/contrib-spi.sgml               |  93 -----
src/tools/msvc/Install.pm                   |   2 +-
8 files changed, 4 insertions(+), 764 deletions(-)