Remove tests that are now dead.

Prefixes + importing records are not implemented presently. When they
are we can re-add support for them.
Trigger errors on deprecated fixture formats.

Update fixtures in tests. Instead of adding shims, Jose and I have
decided it is better to provide features in the UpgradeShell to migrate
fixtures. Fixtures will now trigger errors on known to be old formats.
Add optionparser options for fixtures command.
Add documentation for path argument.

It was undocumented before.
Fix misnamed class.
Implement dirty first pass at upgrading fixture schema.

Uses dirty horrible code, but it works.