State: cleanup code

Remove useless code. change.C is the collection name, which is used to get the collection, which intern is used to set change.C to the collection name.
Ensure metadata file gets closed
Merge pull request #1132 from wallyworld/lp-1392514

Ensure metadata file gets closed

Fixes: https://bugs.launchpad.net/juju-core/+bug/1392514
Merge pull request #1131 from waigani/code-cleanup

State: cleanup code

Remove useless code. change.C is the collection name, which is used to get the collection, which intern is used to set change.C to the collection name.