The state stored in $GIT_DIR/rebase-merge/prev_head was introduced in 58634db (rebase: Allow merge strategies to be used when rebasing,
2006-06-21), but it was never used and should therefore be removed.
Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>