* Change references to tootsuite/mastodon to mastodon/mastodon

* Remove obsolete test fixture

* Replace occurrences of tootsuite/mastodon with mastodon/mastodon in CHANGELOG

And a few other places

I didn't received  the memo, but I just follow the flow.

Signed-off-by: Marcin Mikołajczak <me@m4sk.in>