Drop The Noun Project integration

[quincylvania]

In #5691 we added support for pulling icons from https://thenounproject.com. However, for #7959 we have to replace the request package for downloading icons, which is tricky since TNP requires oauth. To date we only use seven icons, likely since there are a number of drawbacks:

• An account with API tokens is required for downloading icons with iD's build scripts.
• Most icons are not public domain and there's no way to search/filter by license.
• Most icons don't match iD's style requirements.
• The identifiers are numeric and thus aren't descriptive.

I don't think it's worth maintaining this integration for seven icons. We can just add any of the public domain icons to Temaki in order to use them with iD. This also lets us edit the icons as needed, give them descriptive names, and provide them to other projects that use Temaki.