gpcloud: remove PGDLLIMPORT definition
gpcloud: remove PGDLLIMPORT definition

It might cause conflicts, safe to remove once put `PG_MODULE_MAGIC` into
`extern "C"` block.

adam8157/gpdb,cjcjameson/gpdb,Chibin/gpdb,cjcjameson/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb,Chibin/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,lisakowen/gpdb,yuanzhao/gpdb,xinzweb/gpdb,janebeckman/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,50wu/gpdb,janebeckman/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,janebeckman/gpdb,Chibin/gpdb,lisakowen/gpdb,edespino/gpdb,edespino/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,edespino/gpdb,xinzweb/gpdb,xinzweb/gpdb,yuanzhao/gpdb,janebeckman/gpdb,edespino/gpdb,janebeckman/gpdb,jmcatamney/gpdb,Chibin/gpdb,Chibin/gpdb,cjcjameson/gpdb,Chibin/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,Chibin/gpdb,jmcatamney/gpdb,50wu/gpdb,ashwinstar/gpdb,xinzweb/gpdb,50wu/gpdb,edespino/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,janebeckman/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,adam8157/gpdb,jmcatamney/gpdb,janebeckman/gpdb,xinzweb/gpdb,edespino/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,adam8157/gpdb,greenplum-db/gpdb,adam8157/gpdb,janebeckman/gpdb,lisakowen/gpdb,50wu/gpdb,edespino/gpdb,Chibin/gpdb,jmcatamney/gpdb,50wu/gpdb,adam8157/gpdb,edespino/gpdb,Chibin/gpdb,cjcjameson/gpdb,50wu/gpdb,greenplum-db/gpdb,edespino/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,yuanzhao/gpdb,janebeckman/gpdb,yuanzhao/gpdb,adam8157/gpdb,lisakowen/gpdb,cjcjameson/gpdb,xinzweb/gpdb,Chibin/gpdb,adam8157/gpdb,lisakowen/gpdb,janebeckman/gpdb,edespino/gpdb,cjcjameson/gpdb,jmcatamney/gpdb,yuanzhao/gpdb