revert to conda but with libmamba solver

[casperdcl]

• follow-up to docker: fix mamba install #831

diff: https://github.com/SyneRBI/SIRF-SuperBuild/pull/839/files?w=1

[paskino]

What is the difference?

[casperdcl]

What is the difference?

We rely one one less thing, don't have to add FAQs & docs for mamba everywhere, and the conda commands pple expect "just work"

[KrisThielemans]

This is failing on the conda env update --file environment.yml for 3 of the docker builds with (e.g. here

#58 89.21 Collecting package metadata (repodata.json): ...working... done
Error: The operation was canceled.

After 5 hours. Presumably the libmamba-solver didn't help. Sigh.

[casperdcl]

actually as per https://conda.org/blog/2023-11-06-conda-23-10-0-release we can just revert to plain conda>=23.10 now. No need to explicitly use mamba or the libmamba solver.

[paskino]

shall we close this @casperdcl ?

[KrisThielemans]

Yes please. Could do a new but simpler one later as conda now defaults to the mamba solver, but I personally see no good reason to do the effort.