Remove mention of pg_upgrade in release checklist.
Remove mention of pg_upgrade in release checklist.

rvs/gpdb,snaga/postgres-xl,tangp3/gpdb,0x0FFF/gpdb,postmind-net/postgres-xl,pavanvd/postgres-xl,Chibin/gpdb,kaknikhil/gpdb,ahachete/gpdb,jmcatamney/gpdb,yazun/postgres-xl,lpetrov-pivotal/gpdb,ahachete/gpdb,edespino/gpdb,ahachete/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,ovr/postgres-xl,cjcjameson/gpdb,Quikling/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,jmcatamney/gpdb,arcivanov/postgres-xl,randomtask1155/gpdb,oberstet/postgres-xl,yuanzhao/gpdb,janebeckman/gpdb,0x0FFF/gpdb,ovr/postgres-xl,adam8157/gpdb,rvs/gpdb,Chibin/gpdb,ashwinstar/gpdb,Postgres-XL/Postgres-XL,cjcjameson/gpdb,Quikling/gpdb,randomtask1155/gpdb,arcivanov/postgres-xl,kmjungersen/PostgresXL,ashwinstar/gpdb,tpostgres-projects/tPostgres,xuegang/gpdb,chrishajas/gpdb,xinzweb/gpdb,tangp3/gpdb,CraigHarris/gpdb,Quikling/gpdb,ashwinstar/gpdb,pavanvd/postgres-xl,rvs/gpdb,ahachete/gpdb,lpetrov-pivotal/gpdb,atris/gpdb,lpetrov-pivotal/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,kaknikhil/gpdb,chrishajas/gpdb,zaksoup/gpdb,atris/gpdb,ahachete/gpdb,0x0FFF/gpdb,cjcjameson/gpdb,Chibin/gpdb,edespino/gpdb,yuanzhao/gpdb,Quikling/gpdb,tpostgres-projects/tPostgres,xuegang/gpdb,lisakowen/gpdb,zaksoup/gpdb,rvs/gpdb,50wu/gpdb,oberstet/postgres-xl,zeroae/postgres-xl,xinzweb/gpdb,chrishajas/gpdb,yuanzhao/gpdb,atris/gpdb,Quikling/gpdb,adam8157/gpdb,pavanvd/postgres-xl,chrishajas/gpdb,Chibin/gpdb,foyzur/gpdb,kaknikhil/gpdb,lpetrov-pivotal/gpdb,zaksoup/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,kmjungersen/PostgresXL,Postgres-XL/Postgres-XL,kaknikhil/gpdb,foyzur/gpdb,chrishajas/gpdb,lpetrov-pivotal/gpdb,lintzc/gpdb,edespino/gpdb,cjcjameson/gpdb,jmcatamney/gpdb,CraigHarris/gpdb,50wu/gpdb,yazun/postgres-xl,lintzc/gpdb,greenplum-db/gpdb,xuegang/gpdb,jmcatamney/gpdb,zaksoup/gpdb,Quikling/gpdb,lpetrov-pivotal/gpdb,yazun/postgres-xl,Quikling/gpdb,lintzc/gpdb,postmind-net/postgres-xl,kaknikhil/gpdb,0x0FFF/gpdb,techdragon/Postgres-XL,Quikling/gpdb,kmjungersen/PostgresXL,xuegang/gpdb,adam8157/gpdb,tangp3/gpdb,edespino/gpdb,rubikloud/gpdb,rubikloud/gpdb,postmind-net/postgres-xl,oberstet/postgres-xl,chrishajas/gpdb,zeroae/postgres-xl,CraigHarris/gpdb,xinzweb/gpdb,rubikloud/gpdb,kaknikhil/gpdb,janebeckman/gpdb,xuegang/gpdb,janebeckman/gpdb,rubikloud/gpdb,jmcatamney/gpdb,royc1/gpdb,kaknikhil/gpdb,randomtask1155/gpdb,zaksoup/gpdb,xinzweb/gpdb,Chibin/gpdb,lisakowen/gpdb,oberstet/postgres-xl,atris/gpdb,ashwinstar/gpdb,edespino/gpdb,lintzc/gpdb,edespino/gpdb,atris/gpdb,foyzur/gpdb,zeroae/postgres-xl,royc1/gpdb,rubikloud/gpdb,kmjungersen/PostgresXL,CraigHarris/gpdb,arcivanov/postgres-xl,lisakowen/gpdb,cjcjameson/gpdb,janebeckman/gpdb,tpostgres-projects/tPostgres,Quikling/gpdb,tpostgres-projects/tPostgres,edespino/gpdb,lintzc/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,ovr/postgres-xl,rubikloud/gpdb,royc1/gpdb,lintzc/gpdb,xinzweb/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,Postgres-XL/Postgres-XL,rubikloud/gpdb,janebeckman/gpdb,greenplum-db/gpdb,edespino/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,CraigHarris/gpdb,50wu/gpdb,atris/gpdb,snaga/postgres-xl,janebeckman/gpdb,ahachete/gpdb,lisakowen/gpdb,jmcatamney/gpdb,kmjungersen/PostgresXL,cjcjameson/gpdb,rubikloud/gpdb,foyzur/gpdb,adam8157/gpdb,randomtask1155/gpdb,rvs/gpdb,xinzweb/gpdb,yazun/postgres-xl,50wu/gpdb,lintzc/gpdb,atris/gpdb,greenplum-db/gpdb,Chibin/gpdb,postmind-net/postgres-xl,rvs/gpdb,adam8157/gpdb,zaksoup/gpdb,zeroae/postgres-xl,snaga/postgres-xl,zaksoup/gpdb,xinzweb/gpdb,foyzur/gpdb,atris/gpdb,randomtask1155/gpdb,arcivanov/postgres-xl,tpostgres-projects/tPostgres,50wu/gpdb,lisakowen/gpdb,xuegang/gpdb,yazun/postgres-xl,xuegang/gpdb,arcivanov/postgres-xl,ahachete/gpdb,greenplum-db/gpdb,oberstet/postgres-xl,tangp3/gpdb,randomtask1155/gpdb,cjcjameson/gpdb,foyzur/gpdb,randomtask1155/gpdb,lintzc/gpdb,CraigHarris/gpdb,adam8157/gpdb,pavanvd/postgres-xl,rvs/gpdb,50wu/gpdb,techdragon/Postgres-XL,Chibin/gpdb,janebeckman/gpdb,chrishajas/gpdb,greenplum-db/gpdb,50wu/gpdb,0x0FFF/gpdb,adam8157/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,arcivanov/postgres-xl,tangp3/gpdb,yuanzhao/gpdb,royc1/gpdb,foyzur/gpdb,snaga/postgres-xl,Chibin/gpdb,adam8157/gpdb,tangp3/gpdb,tangp3/gpdb,CraigHarris/gpdb,yuanzhao/gpdb,techdragon/Postgres-XL,janebeckman/gpdb,Quikling/gpdb,royc1/gpdb,royc1/gpdb,xinzweb/gpdb,lpetrov-pivotal/gpdb,CraigHarris/gpdb,royc1/gpdb,janebeckman/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,Chibin/gpdb,lisakowen/gpdb,randomtask1155/gpdb,ovr/postgres-xl,xuegang/gpdb,50wu/gpdb,0x0FFF/gpdb,lpetrov-pivotal/gpdb,ahachete/gpdb,ovr/postgres-xl,foyzur/gpdb,kaknikhil/gpdb,tangp3/gpdb,yuanzhao/gpdb,chrishajas/gpdb,jmcatamney/gpdb,rvs/gpdb,lisakowen/gpdb,rvs/gpdb,Postgres-XL/Postgres-XL,0x0FFF/gpdb,rvs/gpdb,Postgres-XL/Postgres-XL,ashwinstar/gpdb,royc1/gpdb,yuanzhao/gpdb,Chibin/gpdb,janebeckman/gpdb,postmind-net/postgres-xl,zaksoup/gpdb,edespino/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,edespino/gpdb,lintzc/gpdb,xuegang/gpdb,snaga/postgres-xl