[CI] Replace pypi deluge-libtorrent with libtorrent

* Remove certifi since included in requirements.txt
* Remove old travis config

.github/workflows/ci.yml

@@ -78,7 +78,7 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v2
         with:
-          python-version: "3.6"
+          python-version: "3.7"
 
       - name: Cache pip
         uses: actions/cache@v2
@@ -92,8 +92,8 @@ jobs:
 
       - name: Install dependencies
         run: |
-          python -m pip install --upgrade pip wheel certifi
-          python -m pip install deluge-libtorrent
+          python -m pip install --upgrade pip wheel
+          python -m pip install libtorrent==1.2.*
           pip install -r requirements.txt -r requirements-tests.txt
           pip install -e .