Unignore muddle.

Refs #11481, #11487.
muddle_users: Nuke redirected imports.

Refs #11487.
muddle_users: Be pyflakes-clean.

Refs #11487.
muddle_users: Remove empty templatetags package.

Refs #11487.
muddle: Fix a load of pyflakes warnings.

Refs #11481, 11487.
muddle: Kill dead code.