Remove fixme comment in aset.c:AllocSetTransferAccounting. (#13786)
Remove fixme comment in aset.c:AllocSetTransferAccounting. (#13786)

As AllocSetTransferAccounting() was called during MemoryContextSetParent().

Before update the memory accouting info, it asserts MemoryContextIsValid(),
which includes AllocSetContext, SlabContext and GenerationContext.

Currently, there is no mixed context situation and other context doesn't have
the accounting info, so I think it's ok to remove the comment.
greenplum-db/gpdb,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb