Update GH actions to only install necessary dependencies

Only install dependencies required for hosting, not cloud functions

.github/workflows/firebase-hosting-pull-request.yml

@@ -11,8 +11,6 @@ jobs:
       - uses: actions/checkout@v2
       - run: npm install
       - run: npm run build
-      - run: cd functions && npm install
-      - run: cd ..
       - uses: FirebaseExtended/action-hosting-deploy@v0
         with:
           repoToken: '${{ secrets.GITHUB_TOKEN }}'