Fix the way GetExistingLocalJoinPath is documented.
Fix the way GetExistingLocalJoinPath is documented.

The old approach made it look like it was an FDW callback, which it
is not.

Per a gripe from Stephen Frost.  Patch by me, reviewed by Ashutosh
Bapat.

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