Fix linux build action [ci build]

We simply upgrade to ubuntu-20.04 since github action ubuntu-18.04 broken on 2021.5.1X

.github/workflows/linux-ci.yml

@@ -18,7 +18,7 @@ jobs:
     # well on Windows or Mac.  You can convert this to a matrix build if you need
     # cross-platform coverage.
     # See: https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/managing-complex-workflows#using-a-build-matrix
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v2
@@ -28,9 +28,7 @@ jobs:
     - name: Create Build Environment
       # Some projects don't allow in-source building, so create a separate build directory
       # We'll use this as our working directory for all subsequent commands
-      run: |
-        for apt_file in `grep -lr microsoft /etc/apt/sources.list.d/`; do sudo rm $apt_file; done
-        tools/travis-scripts/before-install.sh
+      run: tools/travis-scripts/before-install.sh
 
     - name: Build
       # Execute the build.  You can specify a specific target with "--target <NAME>"