input: Write a function to remove all occurrences of the character 'b' from a list.
  assert remove_arr(['a', 'b', 'c', 'b', 'd']) == ['a', 'c', 'd']
  assert remove_arr(['b', 'b', 'b', 'a', 'b']) == ['a']
  assert remove_arr(['a', 'b', 'c', 'd', 'e']) == ['a', 'c', 'd', 'e']
  assert remove_arr(['b', 'b', 'b']) == []
output: def remove_arr(lst):
      return [char for char in lst if char != 'b']