Fixes enum34 not found error when switching Conda environments

💥 BREAKING CHANGE: The ROS dist-packages path is now fully removed from the PYTHONPATH
when inside an Conda environment.

Before:
 ROS environment site-packages folder was placed before the ROS dist-packages path.

After:
 Now the ROS dist-packages folder is removed from the PYTHONPATH when inside an
 anaconda environment.

 This was done as this method caused `module enum34 not found` error when changing
 between Conda Environments