Cleanup comments for `remove_dbtablespaces()`
Cleanup comments for `remove_dbtablespaces()`

In Postgres, `remove_dbtablespaces()` are used for both `createdb()` failure, and
`dropdb()` commit.

In GPDB, persistent tables are used to track the state of the objects, like
table space, database files, etc., and properly clean them up at the end of
transaction (either commit or abort). That's handled by `AtEOXact_smgr()`.

We can safely delete `remove_dbtablespaces()` function. We put the deadcode
under `#if 0` to make future merge easier.

Signed-off-by: Xin Zhang <80ac6425c128040c27b3c6077c824bc26222f5e7@pivotal.io>

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