Prevent check constraint drop on leaf partitions
Prevent check constraint drop on leaf partitions

This commit is part of Add Partitioned Indexes #7047.

Don't allow check constraints to be dropped on partition leaves. Only
allow them to be dropped from the root.

This restriction had been relaxed on PRIMARY KEY and UNIQUE constraints
after adding INTERNAL_AUTO dependencies to constraints. However, we need
to maintain the restiction on check constrants because they are
currently not being protected by pg_depend.

Co-authored-by: Kalen Krempely <9e21ad9b1cb949be1035df9e3f38e74e41b67a0b@pivotal.io>

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