np2: experimental fix for SSG-EG

[jpcima]

Fully experimental attempt to fix Neko SSG-EG

• makes EGUpdate() happen at each step of SSG-EG case generation. observed to fix some cases of audible discontinuities in the envelope

• disables use a formula based on ssg_vector and ssg_offset. those are adjustement values of the EG output from tables, I sincerely don't know too much what they serve for. What I know: it's broken in a way which makes EG level go very low, and makes SSG-EG operators unheard (for example, in case of "Bird Tweet" from xg.wopn)

Having made this edits, the EG sounds much nearer to MAME which I take as reference. Comparison to Nuked is good in case of "Bird Tweet", however "Telephone" has a big difference from OPN2 to OPNA. Still, Neko's "Telephone" seems to lack some of timbral complexity that MAME has. (possibly, to relate with the disabled ssg stuff)

[jpcima]

After checking some more, it needs some work to also reimplement HOLD and ALT modes correctly. Probably why the second is not working correctly.

[Wohlstand]

Checked out, and took! :fox_face: :wink: