delete redundant IteratorSize method for Slices

Already covered as an `AbstractArray` subtype.

Author: nsajko

base/slicearray.jl

@@ -225,7 +225,6 @@ constructed by [`eachcol`](@ref).
 const ColumnSlices{P<:AbstractMatrix,AX,S<:AbstractVector} = Slices{P,Tuple{Colon,Int},AX,S,1}
 
 
-IteratorSize(::Type{Slices{P,SM,AX,S,N}}) where {P,SM,AX,S,N} = HasShape{N}()
 axes(s::Slices) = s.axes
 size(s::Slices) = map(length, s.axes)