Equipment edit: for some reason we need a local copy of index

Calling enableEdition appears to corrupt the index that is passed into
this slot.

This doesn't fix the problem that we can't edit the cylinder start and end
pressure of a manually added dive, but at least we no longer try to edit
and invalid index.

See #582

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Add dive: remove cylinder pressures from samples

These cylinder pressures are actually just artefacts of the way we track
gas consumption in the code shared between planner and add dive. We don't
want them in the actual dive.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>