Unable to leave coach interest list

1. Give a short description of the bug

• Coaches are unable to leave a project's coach interest list

2. Explain the steps you took to trigger the bug

• Go to a project
• Join the coach interest list
• Try to leave the coach interest list

3. What is the expected behavior?

• You are no longer on the coach interest list

4. What is the actual behavior?

• An error message "You are already in the interest list for this project." is shown

This bug also affects the student interest list in the same way.