Delete legacy sectors

[tsmbland]

There's a fair bit of code to do with legacy sectors (e.g. legacy_sector.py, and the calibrate_legacy_sectors function in mca.py). I guess this is included to maintain backwards compatibility, but this code isn't covered by any tests so there's no guarantee it even still works.

If people want to use this feature (very unlikely I would say), then they will always have access to older versions of MUSE. Otherwise, I see no point keeping this code, and it would make my life easier to get rid of it and generally shrink the codebase