pgsql: Remove support for on_exit()

Remove support for on_exit()

All supported platforms support the C89 standard function atexit()
(SunOS 4 probably being the last one not to), and supporting both
makes the code clumsy.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/d383c23f6fbc4a79dae66483cf4f7051121008ad

Modified Files
--------------
configure                     |  209 -----------------------------------------
configure.in                  |    5 -
contrib/pg_upgrade/server.c   |    8 --
src/backend/storage/ipc/ipc.c |   23 +----
src/bin/psql/input.c          |   13 ---
src/include/pg_config.h.in    |    6 -
src/include/pg_config.h.win32 |    6 -
7 files changed, 2 insertions(+), 268 deletions(-)