remove old variables when moving of scales

[jmitrevs]

Description

When moving scales, some old attributes can cause problems and should not be copied. This PR tries to limit the attributes that are copied

Type of change

• Bug fix (non-breaking change that fixes an issue)

Tests

A brevitas example triggered this issue. I am not sure if we should add it to a pytest.

Checklist

• I have read the guidelines for contributing.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have installed and run pre-commit on the files I edited or added.
• I have added tests that prove my fix is effective or that my feature works.

[JanFSchulte]

Tested this locally with a brevitas -> QONNX -> hls4ml workflow that crashes without this PR. With these changes, it works fine.