revert children to use Base.in

oops

Author: ablaom

test/composition/learning_networks/inspection.jl

@@ -13,8 +13,8 @@ List all (immediate) children of node `N` in the ancestor graph of `y`
 
 """
 children(N::AbstractNode, y::AbstractNode) = filter(nodes(y)) do Z
-    t = MMI.isrepresented(N, MLJBase.args(Z)) ||
-        MMI.isrepresented(N, MLJBase.train_args(Z))
+    t = N in MLJBase.args(Z) ||
+        N in MLJBase.train_args(Z)
 end |> unique
 
 @constant X = source()