Revert "Fix test_mulled_build.py::test_mulled_build_files_cli with use_mamba=True"

[bernt-matthias]

Reverts #19545 because it breaks container building since the install location must be the same as the location in the final image (conda environments can not be relocated .. we are just using here that the install location and the location in the final image is the same).

I can't see that the unit test that should be fixed in the referred PR actually ran.

Needs to be backported to 24.0 #19626.

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[kysrpex]

I cannot check this soonish, bit if ir breaks container builds go ahead, broken containers are worse than broken tests

[bernt-matthias]

1974681 should fix the unit test temporarily (until the miniforge container contains mamba>=2.0). mamba-org/mamba#3845

[nsoranzo]

Thanks for investigating this, nice fix!

[martenson]

as I understand it this is not needed since #19714 will be merged forward, please reopen if I'm wrong

[nsoranzo]

Commit 7a4a565 is not part of #19714, reopening.

@bernt-matthias Do you want to rebase it?