Remove Prerequisites

[philipmjohnson]

Please do work for this task in a branch called issue-741.

Review by faculty and advisors led to the conclusion that we should remove prerequisites from the system.

This is a non-trivial task, and involves at least the following:

• Removing the UI components that display prerequisites.
• Removing the prereq fields from courses.
• Removing prereqs data from the database.
• Removing prereqs from the development fixture script.
• Migrating the production system to one that doesn't involve prerequisites.
• Making sure tests are OK.

[cammoore]

Migrating the production system to one that doesn't involve prerequisites might be as simple as:

1. Deploying the new code.
2. Dump the database this won't have corequisites or prerequisites.
3. Reset the db.
4. Load the new data dump.