Remove useless pg_audit.conf
Remove useless pg_audit.conf

No need to have pg_audit.conf any longer since the regression tests are
just loading the module at the start of each session (to simulate being
in shared_preload_libraries, which isn't something we can actually make
happen on the buildfarm itself, it seems).

Pointed out by Tom

adam8157/gpdb,techdragon/Postgres-XL,ashwinstar/gpdb,xinzweb/gpdb,adam8157/gpdb,pavanvd/postgres-xl,yazun/postgres-xl,jmcatamney/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,50wu/gpdb,50wu/gpdb,pavanvd/postgres-xl,oberstet/postgres-xl,adam8157/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,xinzweb/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,greenplum-db/gpdb,ovr/postgres-xl,ashwinstar/gpdb,pavanvd/postgres-xl,xinzweb/gpdb,zeroae/postgres-xl,Postgres-XL/Postgres-XL,lisakowen/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,adam8157/gpdb,lisakowen/gpdb,yazun/postgres-xl,yazun/postgres-xl,techdragon/Postgres-XL,xinzweb/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,greenplum-db/gpdb,adam8157/gpdb,zeroae/postgres-xl,pavanvd/postgres-xl,jmcatamney/gpdb,lisakowen/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,zeroae/postgres-xl,Postgres-XL/Postgres-XL,50wu/gpdb,jmcatamney/gpdb,Postgres-XL/Postgres-XL,ashwinstar/gpdb,yazun/postgres-xl,adam8157/gpdb,yazun/postgres-xl,zeroae/postgres-xl,jmcatamney/gpdb,ovr/postgres-xl,50wu/gpdb,ashwinstar/gpdb,ovr/postgres-xl,ovr/postgres-xl,Postgres-XL/Postgres-XL,jmcatamney/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,zeroae/postgres-xl,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb,lisakowen/gpdb,oberstet/postgres-xl,50wu/gpdb,ovr/postgres-xl,50wu/gpdb,greenplum-db/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,ashwinstar/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,xinzweb/gpdb