Remove lodash flatten and flattenDeep

(re: #6087)

modules/util/array.js

@@ -60,6 +60,17 @@ export function utilArrayChunk(a, chunkSize) {
 }
 
 
+// Flattens two level array into a single level
+// var a = [[1,2,3],[4,5,6],[7]];
+// utilArrayFlatten(a);
+//   [1,2,3,4,5,6,7];
+export function utilArrayFlatten(a) {
+    return a.reduce(function(acc, val) {
+        return acc.concat(val);
+    }, []);
+}
+
+
 // Groups the items of the Array according to the given key
 // `key` can be passed as a property or as a key function
 //