This was a bad idea. Don't free except in the free function.

There is no reason why we need to use a callback here. A string array
fits better with the usage, as this is not an event and we don't need
anything from the user.

When there is a reference in the target namespace, we should overwrite
it. Instead it gets a different name under the current code.

Inside `git_remote_load`, the calls to `get_optional_config` use
`giterr_clear` to unset any errors that are set due to missing config
keys. If neither a fetch nor a push url config was found for a remote,
we should set an error again.

If the remote supports the symref protocol extension, then we return
that, otherwise we guess with git's rules.

When we delete a remote, we also need to go through its fetch refspecs
and remove the references they create locally.

The order in this function is the opposite to what
create_with_fetchspec() has, so change this one, as url-then-refspec is
what git does.

As we need to break compilation and the swap doesn't do that, let's take
this opportunity to rename in-memory remotes to anonymous as that's
really what sets them apart.