Removes all v0 files. these endpoints now return 410 (gone), except for
the download action, which rewrites the url to return a redirect to the v1 api endpoint.

We may consider writing an nginx directive to handle this as it would be
far faster.

Removes some unused imports and adds in a slash that was missiong from
the url being redirected to.

…o ft/remove-v0

Only v0 uses the fetch method on the auth handler. v1 uses the get
method. This removes the fetch method and the tests for it.

validate_path is only used by v0, so by removing v0, we can remove
validate_path as well. validate_v1_path also gets renamed validate_path
to cut down any confusion about the naming

Some tests only tested validate_path, which has been removed, so these
tests were removed. Other tests needed to be updated so that they were
mocked correctly because validate_v1_path (now `validate_path`) makes
network requests.