Remove mpi4py setup in parallel CI jobs

Don't think it should cause a problem, but is unneeded now that we use
OpenMPI from the Julia package manager for the CI jobs, and maybe there
is some conflict that is causing intermittent failures in the parallel
tests.

.github/workflows/debug_checks.yml

@@ -15,9 +15,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: mpi4py/setup-mpi@v1
-        with:
-          mpi: 'openmpi'
       - uses: julia-actions/setup-julia@latest
         with:
           version: '1.10'

.github/workflows/parallel_test.yml

@@ -14,9 +14,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: mpi4py/setup-mpi@v1
-        with:
-          mpi: 'openmpi'
       - uses: julia-actions/setup-julia@latest
         with:
           version: '1.10'
@@ -47,9 +44,6 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: mpi4py/setup-mpi@v1
-        with:
-          mpi: 'openmpi'
       - uses: julia-actions/setup-julia@latest
         with:
           version: '1.10'