Fix Travis CI on 'develop' branch (#877)

* Removed unused code

There is no reason to keep old, unused code in a git repository

* Removed system_site_packages from Travis CI

system_site_packages are opposed to the used conda installation. They are both unnecessary and lead to Travis build errors.

.travis.yml

@@ -9,15 +9,9 @@ sudo: false
 notifications:
   email: false
 
-virtualenv:
-    system_site_packages: true
-
-
 env:
     # Enable python 2 and python 3 builds
-    # Note that the 2.6 build doesn't get flake8, and runs old versions of
-    # Pyglet and GLFW to make sure we deal with those correctly
-    #- PYTHON=2.6 QT=pyqt4 TEST=standard  # 2.6 support ended 
+    # Note that the python 2.6 support ended.
     - PYTHON=2.7 QT=pyqt4 TEST=extra
     - PYTHON=2.7 QT=pyside TEST=standard
     - PYTHON=3.5 QT=pyqt5 TEST=standard
@@ -68,11 +62,6 @@ install:
     - pip install pytest-xdist # multi-thread py.test
     - pip install pytest-cov # add coverage stats
 
-    # required for example testing on python 2.6
-    - if [ "${PYTHON}" == "2.6" ]; then
-        pip install importlib;
-      fi;
-
     # Debugging helpers
     - uname -a
     - cat /etc/issue