travis: Remove before_install stage

Author: tony

.travis.yml

@@ -33,11 +33,6 @@ cache:
   - directories:
     - ~/source
     - ~/build
-before_install:
-  - export PIP_USE_MIRRORS=true
-  - pip install --upgrade pytest  # https://github.com/travis-ci/travis-ci/issues/4873
-  - pip install --upgrade pip wheel virtualenv setuptools
-  - pip install pytest-cov coverage codecov flake8
 install:
   - pip install -e .
   - pip install -r requirements/test.txt