Removing unused parameter rdIterNum

[john-science]

What is the change?

Removed the unused parameter rdIterNum.

Why is the change being made?

This parameter is very specific to one downstream project, and is not used anywhere else. So I judge this Parameter is not useful to a wide enough audience to be in ARMI.

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Checklist

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

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

• The release notes have been updated if necessary.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in pyproject.toml.