Disable fallback on cannonical results file in pg_regress
Disable fallback on cannonical results file in pg_regress

In GPDB, platform_expectfile is used for determining
ORCA/planner/resgroup expect files, wheras in upstream that is not the
case and it is based on the underlying platform. Thus, it is unnecessary
and confusing to compare against default answer file even when
platform_expect file exists. It gets confusing because the below block
chooses the best expect file based on the number of lines in diff file.

Co-authored-by: Ekta Khanna <2fbdcb8e3470ad1f53bbeb24e2deced604b8cfa5@pivotal.io>

greenplum-db/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,jmcatamney/gpdb,lisakowen/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,xinzweb/gpdb,ashwinstar/gpdb,50wu/gpdb,ashwinstar/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,jmcatamney/gpdb,xinzweb/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,adam8157/gpdb,ashwinstar/gpdb,adam8157/gpdb,xinzweb/gpdb,adam8157/gpdb,50wu/gpdb,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,jmcatamney/gpdb