Merge branch 'kn/ref-transaction-symref' into kn/update-ref-symref

* kn/ref-transaction-symref: refs: remove `create_symref` and associated dead code refs: rename `refs_create_symref()` to `refs_update_symref()` refs: use transaction in `refs_create_symref()` refs: add support for transactional symref updates refs: move `original_update_refname` to 'refs.c' refs: support symrefs in 'reference-transaction' hook files-backend: extract out `create_symref_lock()` refs: accept symref values in `ref_transaction_update()`