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?
Maybe? I [asked](https://github.com/JuliaLang/julia/issues/9209#issuecomment-65096323), but didn't get an answer, so I picked the most restrictive. I don't have a better argument than "When is it useful?", so if you think there is a use case, I'll change it.