Unnecessary `toml` dependency

[yousefmoazzam]

There's a dependency on the toml package:

httomo-backends/pyproject.toml

Line 52 in d534eda

"toml",

However, I don't see anywhere in the codebase that this is imported. Also, if I uninstall it from my local dev environment and then:

• run a pipeline with httomo
• or run all httomo-backends tests

I get no error, so I think this dependency isn't needed.