Fixes #3668

Summary/Motivation:

#3668 pointed out that we have some residual files that fail to be deleted after running tests. Because pyomo.duality is entirely deprecated, I'm not touching it, but everything else is resolved.

Changes proposed in this PR:

• Effectively use TempfileManager across tests that were not using it in the past
• There was a double-copyright statement in contrib/sensitivity_toolbox; removed duplicate copyright

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.