github: remove lint jobs for unsupported python versions

.github/workflows/python_lint.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [2.7, 3.5, 3.6, 3.7, 3.8]
+        python-version: [3.6, 3.7, 3.8]
 
     steps:
       - name: Checkout