Merge branch 'jh/update-ref-d-through-symref'

"update-ref -d --deref SYM" to delete a ref through a symbolic ref that points to it did not remove it correctly. * jh/update-ref-d-through-symref: Fix failure to delete a packed ref through a symref t1400-update-ref: Add test verifying bug with symrefs in delete_ref()