MH currently does not support link/invlink properly on a per-variable basis

[torfjelde]

Ref: #1582

Currently, something like

 MH(
       :m => AdvancedMH.StaticProposal(Normal()),
       :s => AdvancedMH.RandomWalkProposal(Normal())
)

won't lead to s being linked as one might except. The "fix" in #1582 makes it so that we at least link if all are RandomWalkProposal.

This could be easily done after TuringLang/DynamicPPL.jl#231 if we decide to take that approach.

Making this issue as a reminder.