`h` ion in HCN1 and HCN2

[Helveg]

HCN1 has ih listed as an ion current USEION h READ eh WRITE ih VALENCE 1
HCN2 has ih listed as a non-specific current NONSPECIFIC_CURRENT ih
This is a little bit dangerous. These 2 mechanisms seem like they would be related via the h ion, but they are not
So each of them can have a separate eh

~ Nora

Let's check what we can do to straighten this out to have the NMODL code reflect the intentions