You wouldn't believe how many KhanUtils we removed!

Summary:
Replace kmath from KhanUtil with kmath from the kmath
repository

Test plan:
 * `make test`
 * `ag 'KhanUtil\.k'` and see no references to KhanUtil.k* in the
   Perseus repo
 * Make a transformer and transform things
 * Make an interactive-graph and drag things
 * make a number-line and drag things
 * make an interaction widget and drag things
 * ugh
 * get fed up with even typing those and stop testing
 * realize that even if we left in a reference to KhanUtil,
   it will work on live (where we have KhanUtil.*) but not in
   dev (since I removed it from the ke-deps-shim), so we can
   find it slowly over time without breaking live.

Auditors: alex