Revert "Merge pull request #113 from jonasdt/cookies_file"

This reverts commit c3a842ec3d7bb62cfdd4b5e56915a9a3233d7b85, reversing
changes made to e68d405cf4331a6f2fd1bd130aa8c97cab75efa5.

This reopens #113, as it broke the authentication for too many courses for
me, when passing many courses in one invocation of `coursera-dl`.