docker/Dockerfile.rocm_ci uses micromamba redundantly

[diptorupd]

The current Dockerfile used for CI is built off a rocm+torch image but then again installs torch in a fresh micromamba env. The pip based install of torch is redundant and the whole use of micromamba can be removed since we already are using a torch-based image.

[diptorupd]

#69 updated the Dockerfile.rocm_ci to use the smaller rocm/dev-ubuntu-${UBUNTU_VERSION}:${ROCM_VERSION}-complete image. The change speeds up the CI builds and also means we can keep using micromamba.