remove mpipy from pip install requirements

An mpi lib file is missing from the currently selected docker image. More testing is needed to support mpi mode for the docker CI.

environment.yml

@@ -33,7 +33,6 @@ dependencies:
   - pytorch::pytorch=2.1
   - pytorch::pytorch-cuda=12.1
   - pip:
-      - mpi4py==3.1.5
       - deepspeed==0.12.4
       - dm-tree==0.1.6
       - git+https://github.com/NVIDIA/dllogger.git