need to consolidate code for vertical scaling of SLA and vcmax

[rgknox]

We have methods that scale SLA over depth:

https://github.com/NGEET/fates/blob/sci.1.72.0_api.33.0.0/biogeochem/FatesAllometryMod.F90#L696

We also have methods that scale vcmax used in photosynthesis, that should match this profile (or at least that is what the intention was). So these two profiles should be synchronized.

https://github.com/NGEET/fates/blob/sci.1.72.0_api.33.0.0/biogeophys/FatesPlantRespPhotosynthMod.F90#L546-L549
https://github.com/NGEET/fates/blob/sci.1.72.0_api.33.0.0/biogeophys/FatesPlantRespPhotosynthMod.F90#L2490

I believe the underlying assumption of these two scaling methods is that leaf nitrogen concentration is constant with leaf area (thus, leaf nitrogen concentration varies over depth).

However, for the former method, if the user sets the min sla to equal the max sla, then they will get no sla scaling over depth.
But the vcmax scaling algorithm is unaffected. This may not be what was originally intended?

I think these algorithms needs a refactor so that that each of them are using shared code for vertical scaling.