Thumbnail rate limit incorrectly applied to non-thumbnail routes

[sarayourfriend]

Description

The thumbnail throttle classes are in the default list of throttles, which are applied to all routes with no explicit throttle classes (which is most of our routes, including search). This means that search requests incorrectly count towards thumbnail requests count, from a throttling perspective.

Reproduction

1. Visit https://api.openverse.engineering/v1/ and check out the response headers and see that `x-ratelimit-limit-anon_thumbnail` is incorrectly present, meaning that throttle class was applied to the request.