Rework Browse by WordCamp list in sidebar of event archives

[BrashRebel]

Check out [an event archive page](​https://wordpress.tv/event/wordcamp-europe-2018/) and scroll down. On the right sidebar there is a "Browse by WordCamp" heading followed by a list of all the terms in the events taxonomy. It's a really long list. There are 699 terms in that taxonomy right now and the list is always growing. We should find a new way for those events to be discovered.

I propose we consider one of the following options:

1. Remove the section entirely. It is not extremely important that we include other events in the sidebar of an event archive. They can be discovered other ways.
2. Convert the list to a dropdown. It would still be a bit tedious to navigate but would be an improvement and would not take up so much space on the page. Plus it would be a pretty simple fix.
3. Implement a search based dropdown. We'd probably need to load a jQuery library or something. I don't believe anything like it already exists on the site's frontend.
4. Create a terms archive page for events, as described in [this ticket](https://meta.trac.wordpress.org/ticket/1434) and link to that page instead of listing the terms there.