Revert "speed up Assignment#representatives"
Revert "speed up Assignment#representatives"

This reverts commit 827f91bb0e2097d101a4bb31f39f9ec1645b1a13.

sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms