Remove our patched copy of Net::HTTP

It's fixed in 6.06.

Removing the patched module infrastructure as there's none left.
Remove use of when/default.  It's experimental in 5.18.
Get the tests working again due to changes in dependencies.

* Net::GitHub::V3 is now using Moo, so we can't subclass it with Mouse.
* Mouse seems to have a problem with type unions with implied class types.