Unbreak sapp CI build (#225)

Summary:
`requirements.txt` is removed in [this commit](4288a95)
The requirements are already automatically installed during setup. Therefore, we don't need to run `pip install -r requirements.txt`, and we can simply remove the line in CI config.
Pull Request resolved: #225

Differential Revision: D19286310

Pulled By: gbleaney

fbshipit-source-id: d64a75bc45bd19376929edd377be5ce83e1e2887

.travis.yml

@@ -17,5 +17,4 @@ jobs:
       install: scripts/travis_install_build_dependencies.sh
       script: ./scripts/setup.sh --local
     - name: "Build and run tests for sapp"
-      install: pip install -r tools/sapp/requirements.txt
       script: cd tools/sapp && python3 setup.py test