Justify or remove `values(::FPlot)`

[jariji]

  values(iterator)

  For an iterator or collection that has keys and values, return an iterator over the
  values. This function simply returns its argument by default, since the elements of
  a general iterator are normally considered its "values".

  values(a::AbstractDict)

  Return an iterator over all values in a collection. collect(values(a)) returns an
  array of values. When the values are stored internally in a hash table, as is the
  case for Dict, the order in which they are returned may vary. But keys(a) and
  values(a) both iterate a and return the elements in the same order.

As discussed in https://github.com/JuliaAPlavin/MakieExtra.jl/issues/5#issuecomment-2319042307 I don't yet see the argument for values(::FPlot) so I think it should either be justified as consistent with Base's definition or removed.

[aplavin]

Yes lots of stuff is experimental in FPlot, very easy to drop some :) I'm always using fplt.data instead.

[aplavin]

Will be removed in the next version.