ci: remove mpi4py action. (#23)

Author: 1uc

.github/workflows/ci.yml

@@ -64,11 +64,6 @@ jobs:
       with:
         submodules: true
 
-    - name: "Setup MPI"
-      uses: mpi4py/setup-mpi@v1
-      with:
-        mpi: openmpi
-
     - name: "Install libraries"
       run: |
         sudo apt-get -qq update