Merge the push report into the refs to avoid a 3rd network call

When @schu and I wrote push, we cheated a little bit and threw in a network call at the end to `info/refs?service=git-receive-pack` to find out what the refs had been updated to, so that `git_remote_ls` would return accurate results immediately after `git_push_finish`.

We left a TODO in place to come back and fix that up later. This PR removes that network call, and uses the push report to update the remote's refs vector. This is faster.