Change pull-local to just be a wrapper for pull with file:///

Change pull-local to just be a wrapper for pull with file:///

This follows up from the previous commit; now that pull knows how to
do the efficient link() or copy for local files, we can just have
pull-local call into ostree_repo_pull().

As part of this:
 - pull() can also accept a file:/// URI instead
   of a remote name (since pull local supports anonymous pulls)
 - pull() knows an "override-remote-name" option, since pull-local
   supported writing a ref out even if there wasn't a remote with
   that name