Remove unused FATES-Hydro parameter

[mpaiao]

It seems the turgor loss point parameter (fates_hydro_pitlp_node) is never actually used in the code. Is this some legacy parameter that could be deleted, or is it something that is planned for future versions of FATES-Hydro?

[jennykowalcz]

I asked @rgknox and @xuchongang about this, and Ryan verified that is is not being used.

[xuchongang]

I looked at the code and @bchristo should have smoothed the PV curves and thus no explicit reference to turgor loss point. @bchristo , can you explain more here? Thank you!