Drop explicit specification of conda environment
Drop explicit specification of conda environment

As we just activate `root` by default, there is no need for an
additional command line argument that specifies `root` to `conda
install`. So just drop this argument.

jakirkham/docker_centos_drmaa_conda,DudLab/docker_centos_drmaa_conda,nanshe-org/docker_centos_drmaa_conda