Remove map JS

[bensteinberg]

This is a follow-up to #3362.

[rebeccacremona]

I think probably this will, on merge, cause another commit of built assets, with an updated webpack-stats.json

[codecov]

Codecov Report

Merging #3363 (a16b0d9) into develop (5c85683) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #3363   +/-   ##
========================================
  Coverage    69.79%   69.79%           
========================================
  Files           50       50           
  Lines         6945     6945           
========================================
  Hits          4847     4847           
  Misses        2098     2098           

[rebeccacremona]

My above prediction was, of course, wrong: since we DID remove the entrypoint from webpack config in the first PR, the change to the stats file subsequent to that PR was sufficient