Use the improved duration and average depth for everything

The code was written to get the SAC rate correct, but we probably do
want to have the duration and mean depth of the dive always be shown for
the non-surface-time.

So move the code from the sac-rate calculation to the generic dive fixup
part.  This makes the dive list and statistics all show the duration as
the under-water duration, which is not necessarily the same as
"difference between beginning and end of dive".

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>