Make sure there's no ${HOME}/.conda dir

[yuvipanda]

Currently, when installing miniconda we end up with a ${HOME}/.conda directory, with an environments.txt file. This is apparently to help sysadmins on multi user systems discover all the environments users have created on the system (from conda/conda#6748 (comment)). We don't really need that inside a container...

Having ~/.conda present causes problems when REPO_DIR isn't $HOME, since we then don't explicitly recursively chown it.