refactor(syft_exc): replace `PySyftException` with `SyftException`

[tcp]

Description

• Replaces PySyftException with SyftException
• Removes PySyftException from node handler

How has this been tested?

• Current tests are green

Checklist

• [x] I have followed the Contribution Guidelines and Code of Conduct
• [x] I have commented my code following the OpenMined Styleguide
• [x] I have labeled this PR with the relevant Type labels
• [x] My changes are covered by tests