input: Write a function to remove all occurrences of a given element in a given array and return the modified array. If the array is empty, it should return an empty array.
  assert remove_element([2, 4, 5, 7, 4, 2], 4)==[2, 5, 7, 2]
  assert remove_element([3, 3, 3, 3, 3], 3)==[]
  assert remove_element([1, 2, 3, 4], 5)==[1, 2, 3, 4]
  assert remove_element([], 4)==[]
  assert remove_element([1, 2, 3, 4], None)==[1, 2, 3, 4]
output: def remove_element(arr, elem):
      return [x for x in arr if x != elem]