chore: simplify deployment workflow by removing deprecated OS version

Author: alexperez

.github/workflows/deployment.yml

@@ -18,7 +18,6 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04]
-        # os: [ubuntu-18.04, ubuntu-20.04]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2