fix(travis): Remove unnecessary commands

.travis.yml

@@ -14,12 +14,6 @@ services:
 
 install:
   # fix mongodb travis error
-  - sudo rm /etc/apt/sources.list.d/mongodb*.list
-  - pip install flake8==3.3.0
-  - flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics
-  - sudo rm /etc/apt/sources.list.d/docker.list
-  - sudo apt-get install hhvm && rm -rf /home/travis/.kiex/
-  - sudo apt-get purge -y mysql-common mysql-server mysql-client
   - nvm install 10
   - pip install python-coveralls
   - wget https://raw.githubusercontent.com/frappe/bench/master/playbooks/install.py