input: Write a function to remove all occurrences of a given element from a given array. If the given array is empty then return an empty array.
  assert remove_element([2, 4, 5, 7, 4, 2], 4)==[2, 5, 7, 2]
  assert remove_element([1, 1, 2, 2, 1, 3], 2)==[1, 1, 1, 3]
  assert remove_element([4, 4, 4, 4, 4], 4)==[]
  assert remove_element([], 5)==[]
output: def remove_element(arr, elem):
      return [x for x in arr if x != elem]