* Fix default http message handler for watchOS.
Fix default http message handler for watchOS to be NSUrlSessionHandler (the
previous attempt at eb7c2fd was quite incomplete), and make sure
HttpClientHandler is never used (show errors if someone tries).
* [tests] Remove explicit http client handler from project files.
Just use the default instead, since the set of valid http client handlers varies between platforms.
Rolf Bjarne Kvinge