This is useful to send to the client while we're performing the work.

The reporting function has a force parameter which makes sure that we
do send out the message of 100% completed, even if this comes before the
next udpate window.

Set a callback for the packbuilder so we can send the sideband messages
to the caller, formatting them as git would.

This lets us see what the server (or libgit2 locally) is doing, rather
than having to stare at a non-moving screen.

Remove the configuration state we keep in the remote

We're down to simply having it be a call to create_internal() so let's
simply do that. The rest of the code is just a distraction.

It has now become a no-op, so remove the function and all references to
it.

The base refspecs changing can be a cause of confusion as to what is the
current base refspec set and complicate saving the remote's
configuration.

Change `git_remote_add_{fetch,push}()` to update the configuration
instead of an instance.

This finally makes `git_remote_save()` a no-op, it will be removed in a
later commit.