apply: remove `newfd` from `struct apply_state`

apply: remove `newfd` from `struct apply_state`

Similar to a previous patch, we do not need to use `newfd` to signal
that we have a lockfile to clean up. We can just unconditionally call
`rollback_lock_file`. If we do not hold the lock, it will be a no-op.

Where we check `newfd` to decide whether we need to take the lock, we
can instead use `is_lock_file_locked()`.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>