demo: Drop previous "default enabled" logic (experiment remainder)

demo: Drop previous "default enabled" logic (experiment remainder)

A previous implementation of the demo driver supported the creation of
larger channel counts yet only enabling part of them by default. This
was kind of pointless, I just was not aware of the available scan
options.

Drop the "enabled channels" limitation, enable all channels that get
created (like the implementation before the experiment did), and create
as many channels as was compiled in by default or later got specified
by scan options.