Removing references to broken import path

[john-science]

Description

There are some faulty, fictitious import paths in ARMI, particularly ARMI documentation. And this PR removes those.

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[opotowsky]

Oof, much needed! Good job.