Remove restriction to INSERT/UPDATE/DELETE foreign relations (#6202)
Remove restriction to INSERT/UPDATE/DELETE foreign relations (#6202)

- While spiking on implementing PXF using FDW,
  we noticed that error messages for file_fdw
  were different from upstream error messages
  when updating a file_fdw. GPDB introduced a
  check in `setTargetTable` for foreign relations
  that might have not been cleaned up during
  merge. This PR removes the check in `setTargetTable`
  and fixes the expected output in file_fdw.
  Running make installcheck on file_fdw, now
  succeeds, as we are matching the upstream
  error message "updates aren't supported".

Authored-by: Francisco Guerrero <356157bf781222c6d0cb68cd14cecdf57676bd4b@pivotal.io>
lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,adam8157/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,lisakowen/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,xinzweb/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,xinzweb/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,ashwinstar/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb