rebase: stop reading and writing unnecessary strategy state

rebase: stop reading and writing unnecessary strategy state

The state files for "--strategy" and "--strategy-option" are written and
read twice, once by builtin/rebase.c and then by sequencer.c. This is an
artifact of the scripted rebase and the need to support "rebase
--preserve-merges". Now that "--preserve-merges" no-longer exists we
only need to read and write these files in sequencer.c. This enables us
to remove a call to free() in read_strategy_opts() that was added by
f1f4ebf432 (sequencer.c: fix "opts->strategy" leak in
read_strategy_opts(), 2022-11-08) as this commit fixes the root cause of
that leak.

There is further scope for removing duplication in the reading and
writing of state files between builtin/rebase.c and sequencer.c but that
is left for a follow up series.

Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>