remove Flux.flatten in favor of MLUtils.flatten (#2188)

perf/vgg.jl

@@ -38,7 +38,7 @@ function vgg16()
         Conv((3, 3), 512 => 512, relu, pad=(1, 1), stride=(1, 1)),
         BatchNorm(512),
         MaxPool((2,2)),
-        flatten,
+        Flux.flatten,
         Dense(512, 4096, relu),
         Dropout(0.5),
         Dense(4096, 4096, relu),

src/layers/stateless.jl

@@ -1,30 +1,3 @@
-"""
-    flatten(x::AbstractArray)
-
-Reshape arbitrarly-shaped input into a matrix-shaped output,
-preserving the size of the last dimension.
-
-See also [`unsqueeze`](@ref).
-
-# Examples
-```jldoctest
-julia> rand(3,4,5) |> Flux.flatten |> size
-(12, 5)
-
-julia> xs = rand(Float32, 10,10,3,7);
-
-julia> m = Chain(Conv((3,3), 3 => 4, pad=1), Flux.flatten, Dense(400 => 33));
-
-julia> xs |> m[1] |> size
-(10, 10, 4, 7)
-
-julia> xs |> m |> size
-(33, 7)
-```
-"""
-function flatten(x::AbstractArray)
-  return reshape(x, :, size(x)[end])
-end
 
 """
     normalise(x; dims=ndims(x), ϵ=1e-5)