Tidy-up UnsteadySystem class

Issue/feature addressed

This is a tidy-up of the UnsteadySystem class. Notably unused member variables have been removed and GetComm()->GetSpaceComm()->AllReduce is used when relevant.

Proposed solution

• Unused member variable m_nanSteps has been removed.
• Unused member variable m_cflNonAcoustic has been removed.
• Unused member variable m_StagesPerStep has been removed.
• Unused member variable m_filterTimeWarning has been removed.
• Unused member variable m_timestepMax has been removed.
• Unused member variable m_TotLinItePerStep has been removed.
• Unused member variable m_steadyStateRes0 has been removed.
• Unused member variable m_steadyStateRes has been removed.
• Member variable m_magnitdEstimat has been moved to CompressibleFlowSystemImplicit.h
• Member variable m_TimeIntegLambda has been moved to CompressibleFlowSystemImplicit.h
• Member variable m_inArrayNorm has been moved to CompressibleFlowSystemImplicit.h
• Use GetComm()->GetSpaceComm()->AllReduce when relevant.

Implementation

A more detailed description of the changes. Please include any details necessary for reviewers to understand your work, and point out particular points would like them to pay particular attention to.

Tests

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Notes

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Checklist

• Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).