Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

1. The output isn't great. It can be hard to find hotspots and, even
   when you do find them, to find why those are hotspots.
2. It uses some jQuery-specific frontend code which we can remove now
   that we don't have this any more.
3. It's only possible to profile the initial request, not any subsequent
   AJAX requests.

This uses an ActiveRecord subscriber to get queries and calculate the
total query time from that. This means that the total will always be
consistent with the queries in the table. It does however mean that we
could potentially miss some queries that don't go through ActiveRecord.

Making this change also allows us to unify the response JSON a little
bit, making the frontend slightly simpler as a result.

It has a lot of files because that's the point

Removes ce to ee differences for snowplow file

It takes a lot of lines to move a script

pdf.js is available on npm. Importing the dependency from there instead
of vendoring it has certain benefits, e.g. the discoverability of
updates (especially security fixes).

This reverts commit a5378665.