Run clang-format from the system installation instead of pipenv

[codeboy5]

Description

This PR removes clang-format as a Pip dependency and updates the Makefile to run clang-format from the system clang-format installation. Fixes #215

Affected Dependencies

List any dependencies that are required for this change.

How has this been tested?

Running make format-style-cpp does work.

Checklist

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

[chinmayshah99]

Is installing clang-format part of prereqs_linux.sh and prereqs_mac.sh?

[codeboy5]

Is installing clang-format part of prereqs_linux.sh and prereqs_mac.sh?

It was never a part of it, we could update it tho.

[chinmayshah99]

Please do