Also clean up unused PRS1 channels and fix a regression from
9a25647c that broke unintentional leak calculation for CPAP/APAP.
Also add PRS1PressureAverageEvent to F0V4 list of supported events.
Right now this results in slightly confusing graphs, since sometimes
the IPAP/EPAP data for a machine is primarily reported by its settings
events, and for other machines by its statistics events. Also, the
"average" pressure on F0 looks like it might be effectivley EPAP in
single-pressure mode rather than the true average in bi-level mode.
Once we decide on the best presentation, we can either update the importer
or the display to show the most helpful channels for a given session.
