Remove comment referring to non-existent function.
Remove comment referring to non-existent function.

I removed pathnode_copy_node() in an earlier commit, but missed this
comment. If someone needs to copy a Path in the future, they'll have to
come up with a way to do it at that point, but there hasn't been any need
for that so far. (copyObject() should work, but it makes a deep copy, while
the old pathnode_copy_node() function made a shallow copy.

janebeckman/gpdb,adam8157/gpdb,xuegang/gpdb,atris/gpdb,0x0FFF/gpdb,CraigHarris/gpdb,lintzc/gpdb,rvs/gpdb,ashwinstar/gpdb,0x0FFF/gpdb,foyzur/gpdb,Chibin/gpdb,atris/gpdb,lisakowen/gpdb,rvs/gpdb,ashwinstar/gpdb,rvs/gpdb,CraigHarris/gpdb,randomtask1155/gpdb,edespino/gpdb,greenplum-db/gpdb,edespino/gpdb,50wu/gpdb,rubikloud/gpdb,tangp3/gpdb,xinzweb/gpdb,lintzc/gpdb,Chibin/gpdb,yuanzhao/gpdb,royc1/gpdb,lisakowen/gpdb,yuanzhao/gpdb,50wu/gpdb,janebeckman/gpdb,CraigHarris/gpdb,ahachete/gpdb,ashwinstar/gpdb,kaknikhil/gpdb,lpetrov-pivotal/gpdb,ashwinstar/gpdb,Chibin/gpdb,adam8157/gpdb,Quikling/gpdb,Chibin/gpdb,zaksoup/gpdb,cjcjameson/gpdb,janebeckman/gpdb,lisakowen/gpdb,chrishajas/gpdb,edespino/gpdb,xinzweb/gpdb,tangp3/gpdb,rvs/gpdb,royc1/gpdb,adam8157/gpdb,rvs/gpdb,atris/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,0x0FFF/gpdb,foyzur/gpdb,jmcatamney/gpdb,lpetrov-pivotal/gpdb,zaksoup/gpdb,lpetrov-pivotal/gpdb,lpetrov-pivotal/gpdb,lisakowen/gpdb,kaknikhil/gpdb,ahachete/gpdb,CraigHarris/gpdb,randomtask1155/gpdb,Chibin/gpdb,foyzur/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,Chibin/gpdb,greenplum-db/gpdb,atris/gpdb,xinzweb/gpdb,tangp3/gpdb,tangp3/gpdb,ashwinstar/gpdb,CraigHarris/gpdb,lintzc/gpdb,janebeckman/gpdb,jmcatamney/gpdb,chrishajas/gpdb,rubikloud/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,janebeckman/gpdb,50wu/gpdb,CraigHarris/gpdb,Quikling/gpdb,royc1/gpdb,lintzc/gpdb,xinzweb/gpdb,ahachete/gpdb,Quikling/gpdb,tangp3/gpdb,50wu/gpdb,tangp3/gpdb,cjcjameson/gpdb,tangp3/gpdb,foyzur/gpdb,kaknikhil/gpdb,50wu/gpdb,rvs/gpdb,rvs/gpdb,adam8157/gpdb,zaksoup/gpdb,foyzur/gpdb,lisakowen/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,zaksoup/gpdb,cjcjameson/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,xinzweb/gpdb,randomtask1155/gpdb,0x0FFF/gpdb,rubikloud/gpdb,atris/gpdb,royc1/gpdb,kaknikhil/gpdb,zaksoup/gpdb,edespino/gpdb,lpetrov-pivotal/gpdb,royc1/gpdb,rvs/gpdb,janebeckman/gpdb,xuegang/gpdb,rubikloud/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,jmcatamney/gpdb,lpetrov-pivotal/gpdb,edespino/gpdb,adam8157/gpdb,rubikloud/gpdb,adam8157/gpdb,xuegang/gpdb,cjcjameson/gpdb,chrishajas/gpdb,lintzc/gpdb,cjcjameson/gpdb,rvs/gpdb,edespino/gpdb,chrishajas/gpdb,CraigHarris/gpdb,zaksoup/gpdb,edespino/gpdb,lisakowen/gpdb,ahachete/gpdb,Chibin/gpdb,yuanzhao/gpdb,janebeckman/gpdb,atris/gpdb,yuanzhao/gpdb,Chibin/gpdb,xuegang/gpdb,janebeckman/gpdb,chrishajas/gpdb,0x0FFF/gpdb,royc1/gpdb,lintzc/gpdb,yuanzhao/gpdb,Quikling/gpdb,0x0FFF/gpdb,Quikling/gpdb,yuanzhao/gpdb,atris/gpdb,randomtask1155/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,Chibin/gpdb,xinzweb/gpdb,lintzc/gpdb,cjcjameson/gpdb,foyzur/gpdb,kaknikhil/gpdb,50wu/gpdb,xuegang/gpdb,Quikling/gpdb,randomtask1155/gpdb,xuegang/gpdb,yuanzhao/gpdb,lintzc/gpdb,ahachete/gpdb,CraigHarris/gpdb,lisakowen/gpdb,royc1/gpdb,greenplum-db/gpdb,randomtask1155/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,lintzc/gpdb,kaknikhil/gpdb,rubikloud/gpdb,janebeckman/gpdb,zaksoup/gpdb,tangp3/gpdb,rubikloud/gpdb,lpetrov-pivotal/gpdb,ahachete/gpdb,atris/gpdb,adam8157/gpdb,ahachete/gpdb,foyzur/gpdb,xuegang/gpdb,xuegang/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,adam8157/gpdb,greenplum-db/gpdb,janebeckman/gpdb,edespino/gpdb,0x0FFF/gpdb,foyzur/gpdb,Quikling/gpdb,lisakowen/gpdb,randomtask1155/gpdb,Chibin/gpdb,xuegang/gpdb,Quikling/gpdb,0x0FFF/gpdb,royc1/gpdb,50wu/gpdb,lpetrov-pivotal/gpdb,zaksoup/gpdb,chrishajas/gpdb,kaknikhil/gpdb,50wu/gpdb,chrishajas/gpdb,edespino/gpdb,xinzweb/gpdb,CraigHarris/gpdb,ahachete/gpdb,Quikling/gpdb,kaknikhil/gpdb,randomtask1155/gpdb,Quikling/gpdb,chrishajas/gpdb,edespino/gpdb,rubikloud/gpdb,xinzweb/gpdb,rvs/gpdb