remove load_labelled_volume

[alessandrofelder]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?
We have a circular dependency (and can therefore not publish to conda-forge)

What does this PR do?
Removes brainglobe-utils dependent code (which was unused in this package or this org).

References

Closes #256

How has this PR been tested?

Local and CI pytest.
Searched for the removed function across the BrainGlobe GH organisation - it isn't used in not-archived repos.

Is this a breaking change?

Yes, if there are packages outside BrainGlobe depending on the load_labelled_volume, they will need to switch to the load_any function

Does this PR require an update to the documentation?

I am hoping it's sufficient we document image_io.load_any well (which we do!) and use that as our default nrrd file loader.

Checklist:

• The code has been tested locally
• [N/A] Tests have been added to cover all new functionality (unit & integration)
• [N/A] The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[willGraham01]

This'll need a new release to PyPI, which I'll publish after merging this in.

The minor version bump should go trickle through to the rest of the tool-suite automatically (the meta-package should take the most recent version), but it's probably worth pinning any of our packages that depend on atlasapi from below the next time they have a PR merged in.