remove composer install step

we do this again later inside the multidev that we clone down, so there's no reason to do this before we create the multidev

.github/workflows/sage-test.yml

@@ -74,8 +74,6 @@ jobs:
             fi
             # Test that terminus works...
             terminus --version
-      - name: Install Composer Dependencies
-        run: composer install --no-progress --no-suggest --prefer-dist
       - name: Validate Pantheon Host Key
         run: |
           echo "Host *.drush.in HostKeyAlgorithms +ssh-rsa" >> ~/.ssh/config