Deprecate prevind(::Any, ::Integer)

See discussion in #9209 

It seems likely that users that trigger the deprecation rather would have a `MethodError`, and the suggestion to use `i-1` instead is probably bad advise. What do people think?
I think it makes more sense to use `AbstractArray` here; e.g. potentially there could be some sparse matrixes that would overload `prevind` where this would be useful.