Remove psiresp.testing

[lilyminium]

psiresp.testing is a bad hack for patching QCFractal behaviour, making psiresp not quite independent.

~~Once the following issues are resolved, I need to check why I had to replace the storage in FractalSnowflake~~

I had to replace this because FractalSnowflake calls TemporaryPostgres calls PostgresHarness. So we are all clear to remove once issues are gone.

Steps to remove psiresp.testing:

• [ ] delete the file
• [ ] update the tests
• [ ] update the examples and documentation (!!)
• [ ] update environment pins

Issues:

• [ ] https://github.com/MolSSI/QCFractal/issues/698
• [ ] https://github.com/MolSSI/QCFractal/issues/697
• [ ] https://github.com/MolSSI/QCFractal/issues/696