Delete nightlytests.yml

.github/workflows/nightlytests.yml

-name: Build, test and push sim mode container
-on:
-  schedule:
-    - cron: "*/10 * * * *"
-jobs:
-  build:
-    runs-on: ubuntu-18.04
-    env:
-        DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
-        DOCKER_PASSWORD: ${{ secrets.DOCKER_PASSWORD }}
-    steps:
-    - uses: actions/checkout@v1
-    - name: submodule update
-      run: git submodule update --init --recursive
-    - name: build container for testing
-      run: python3 scripts/docker_build.py DockerfileSimulation sgxwalletsim ${GITHUB_SHA}
-    - name: test
-      run: python3 scripts/docker_test.py DockerfileSimulation sgxwalletsim
-
-