Plot pressure data based on 'struct plot_info' rather than raw dive data

Plot pressure data based on 'struct plot_info' rather than raw dive data

Further movement to using the sanitized and cleaned-up plot info rather
than the raw data.

The raw dive data contains samples from the end of the dive that we
don't want to drop, but that we also don't want to actually use for
plotting the dive.  So the eventual end goal here is to not ever use the
raw dive samples directly for plotting, but use the diveplot data that
we have analyzed for min/max (properly ignoring final entries) etc.

There's still some data that we take from the samples when plotting, but
it's getting rarer.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>