[SU10] Disabling thermals at wind speed zero is incorrect

Some confusion seems to have arisen in SU10 regarding “turbulence”, “gusts”
and “thermals”. It makes sense to reduce gusts (and possibly ‘turbulence’ if
that is actually a thing in the sim), but it makes no physical sense at all to
disable thermals (columns of solar-heated air rising from the ground) when the
wind speed reduces 3 knots … 0 knots so this is going to confuse the gliding
capability. In reality any wind/gusts is likely to disrupt thermals a little
bit (but not much, until the winds get really high) and zero wind is probably
optimal for the most organised thermals. There’s no physical rationale that
supresses thermals when the wind reduces. It would be helpful to understand
the objective for the change - if it’s to reduce the confusion for power
pilots then an accessibility slider might make more sense, of if it’s to
disable the weather so dev flight testing is easier there’s probably a more
technical way to do that (WEATHER_DISABLED simvar?) without impacting normal
use of the sim.