pgsql: Remove flatfiles.c, which is now obsolete.

Log Message:
-----------
Remove flatfiles.c, which is now obsolete.

Recent commits have removed the various uses it was supporting. It was a
performance bottleneck, according to bug report #4919 by Lauris Ulmanis; seems
it slowed down user creation after a billion users.

Modified Files:
--------------
pgsql/src/backend/access/transam:
twophase_rmgr.c (r1.8 -> r1.9)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/twophase_rmgr.c?r1=1.8&r2=1.9)
xact.c (r1.274 -> r1.275)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xact.c?r1=1.274&r2=1.275)
xlog.c (r1.350 -> r1.351)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c?r1=1.350&r2=1.351)
pgsql/src/backend/commands:
dbcommands.c (r1.225 -> r1.226)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/dbcommands.c?r1=1.225&r2=1.226)
user.c (r1.187 -> r1.188)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/user.c?r1=1.187&r2=1.188)
vacuum.c (r1.391 -> r1.392)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/vacuum.c?r1=1.391&r2=1.392)
pgsql/src/backend/libpq:
hba.c (r1.189 -> r1.190)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/hba.c?r1=1.189&r2=1.190)
pgsql/src/backend/tcop:
postgres.c (r1.572 -> r1.573)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.572&r2=1.573)
pgsql/src/backend/utils/init:
Makefile (r1.22 -> r1.23)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/init/Makefile?r1=1.22&r2=1.23)
pgsql/src/bin/initdb:
initdb.c (r1.172 -> r1.173)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/initdb/initdb.c?r1=1.172&r2=1.173)
pgsql/src/include/access:
twophase_rmgr.h (r1.7 -> r1.8)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/access/twophase_rmgr.h?r1=1.7&r2=1.8)
pgsql/src/include/catalog:
pg_proc.h (r1.549 -> r1.550)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h?r1=1.549&r2=1.550)

Removed Files:
-------------
pgsql/src/backend/utils/init:
flatfiles.c
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/init/flatfiles.c)
pgsql/src/include/utils:
flatfiles.h
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/flatfiles.h)