bisect--helper: retire `--next-all` subcommand

bisect--helper: retire `--next-all` subcommand

The `--next-all` subcommand is no longer used from the git-bisect.sh
shell script. Instead the function `bisect_next_all()` is called from
the C implementation of `bisect_next()`.

Mentored-by: Lars Schneider <redacted>
Mentored-by: Christian Couder <redacted>
Signed-off-by: Pranit Bauva <redacted>
Signed-off-by: Tanushree Tumane <redacted>
Signed-off-by: Miriam Rubio <redacted>
Reviewed-by: Johannes Schindelin <redacted>
Signed-off-by: Junio C Hamano <redacted>