Remove psutil after orca removal

[dplarson]

The package psutil was originally added as a dependency in PR #359 when converting the codebase to use plotly, where psutil seems to have come from using orca with plotly. However, since then the codebase has moved to plotly >= 4.9, which includes Kaleido as an alternative to Orca. And while previous PRs have already shifted the underlying code to use Kaleido and remove Orca, the requirements.txt and setup.py files still have psutil as a dependency.

Keeping psutil wouldn't necessarily cause any issues, but it's good practice to remove dependencies that are no longer used. And right now, psutil is the only (obvious) unnecessary dependency.

[dplarson]

For further context, this extra psutil dependency came up while I was doing some security hardening of the Docker build and deployment pipelines for running the Arbiter in Kubernetes (part of the process for hosting the Arbiter). Removing psutil hasn't caused any issues in practice from my tests, including building and deploying sfa-api and sfa-dashboard. So while I still expect to do more checks via a PR, I'm pretty confident removing psutil at this point is fine.