[Bug]: COMP SCI 570 and COMP SCI 270 are listed as prerequisites for each other

[gjsorrell]

On the course website for CS 570, it says "Not open to students who have completed COMP SCI 270" and vice versa for CS 270. The web scraper simply reads the link for each class and includes them as prereqs for each other.

Steps To Reproduce

1. Add COMP SCI 570 to flow
2. Add COMP SCI 270 to flow

The current behavior

CS 570 is a prereq for CS 270 and vice versa, creating a cycle.

The expected behavior

Neither should be listed in each other's prereq list. The scraper should read "Not open to students who have completed ____" and ignore the courses listed in that sentence.