Alban Gruin authored May 28, 2018 and Junio C Hamano committed Jun 01, 2018

This removes the code coming from git-rebase--interactive.sh that is not
needed by preserve-merges, and changes the header comment accordingly.

In a following commit, the -p code from git-rebase--interactive.sh will
be stripped out. As preserve-merges’ successor is already in the works,
this will be the only script to be converted.

This also seems to fix a bug where a failure in
`pick_one_preserving_merges()` would fallback to the non-preserve-merges
`pick_one()`.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>