transaction: make map a private attribute
This is used to track which files are modified. It is an
implementation detail of current transactions and doesn't need
to be exposed to the public interface. So mark it as private.
Differential Revision: https://phab.mercurial-scm.org/D4632
transaction: make report a private attribute
This is a callable used for logging. It isn't used outside the
transaction code. It doesn't need to be part of the public interface.
Let's mark it as private.
Differential Revision: https://phab.mercurial-scm.org/D4631