88 remove old code

[maho3]

Removes various legacy code that was either used in early versions of ltu-ili or for private projects. Addresses the following tasks from Issue #88 :

• Remove any temporary scripts from the main branch (e.g. the ones used for private projects).
• Remove the Cosmology object and related tests.

Note, all this code is being removed from the main branch, but is preserved in branch backup_2023-20-11.

[DeaglanBartlett]

Looks good to me, except one small required change in tests/run.sh as we no longer create the file .coverage_utils so cannot merge this file with others when merging the coverage reports.

[maho3]

Note, this PR now also addresses "Make Nicolas' test notebooks consistent with the new version of ltu-ili, or otherwise remove them" from Issue #88 .