Change `lock_raw_ref()` and `lock_ref_sha1_basic()` to use
`refs_verify_refname_available()` instead of
`verify_refname_available_dir()`. This means that those callsites now
check for conflicts with all references rather than just packed refs,
but the performance cost shouldn't be significant (and will be
regained later).
These were the last callers of `verify_refname_available_dir()`, so
also delete that (very complicated) function.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>