MAINTENANCE: Automated closing of pull requests.

This commit exists to close the following pull requests on Github:

Closes #3490 (close requested by 'andrewor14')
Closes #4646 (close requested by 'srowen')
Closes #3591 (close requested by 'andrewor14')
Closes #3656 (close requested by 'andrewor14')
Closes #4553 (close requested by 'JoshRosen')
Closes #4202 (close requested by 'srowen')
Closes #4497 (close requested by 'marmbrus')
Closes #4150 (close requested by 'andrewor14')
Closes #2409 (close requested by 'andrewor14')
Closes #4221 (close requested by 'srowen')