Revert "Adds test to demonstrate that LWP::UserAgent is not currently supported."

This reverts commit 5e64bb696711cbd791053e41485691f3fedde105.
Allow domain and version of the API url to be settable via
MetaCPAN::Client.

The docs say you can set these in the request object directly, but they
also say MetaCPAN::Client->request is for internal use.  It would be
easier if these attributes were settable when creating a new client,
just as the UA is.