Remove MacOS workarounds (#477)

MPICH 3.4 should have fixed pmodels/mpich#4710

Author: simonbyrne

.github/workflows/UnitTests.yml

@@ -20,13 +20,11 @@ jobs:
             julia_arch: x86
         include:
           - os: macos-latest
-            mpiexec_args: "-host localhost"
 
       fail-fast: false
 
     runs-on: ${{ matrix.os }}
     env:
-      MPICH_INTERFACE_HOSTNAME: localhost
       JULIA_MPIEXEC_ARGS: ${{ matrix.mpiexec_args }}
 
     steps: