Refactor graphie's KhanUtil::getDistance

Summary:
Remove's the custom 2D distance in graphie's KhanUtil::getDistance in favor of
delegating to kpoint.distanceToPoint. This still must be wrapped in a function
because kpoint will not be defined at file-run-time in khan-exercises.

This also uncomments the on graphieLoad logic to load k* math utils. This
previously didn't work, but was fixed in
c8f6fd9056144bc434be5c0286d95f70bafefaf1

Test Plan:
visit /exercises/congruency_postulates.html and make sure it is still solvable
with no javascript errors.

Auditors: alex