Remove meck in favor of an API stub

[rbishop]

Using meck for mocking is kind of weird and unnatural. It's easier and cleaner to just stand up a simple Plug app with a notify route and change the origin config for the test environment. We will probably also need to add Cowboy as a test dependency.

[joshuap]

👍

[dpehrson]

@rbishop @joshuap It may be worth looking into Bypass

I've used it a bit and while there is room for improvement, if you're not doing anything that requires coordinating lots of outgoing requests, it's probably a lighter weight solution.

Edit: Just realized this was a pretty old issue, I just saw it and figured I'd offer a suggestion.