Your goal in this is to implement a difference function, which subtracts one list from another and returns the result.
It should remove all values from list a, which are present in list b.
array_diff([1,2],[1]) == [2]
If a value is present in b, all of its occurrences must be removed from the other:
array_diff([1,2],[1]) == [2]
Create a method called array_diff that accepts two arrays.