input: Write a python function to remove all occurrences of a character 'x' from a list.
  assert remove_x(['a', 'x', 'b', 'x', 'c', 'x']) == ['a', 'b', 'c']
  assert remove_x(['x', 'x', 'x', 'd', 'e', 'f']) == ['d', 'e', 'f']
  assert remove_x(['g', 'h', 'i', 'x', 'x', 'x']) == ['g', 'h', 'i']
output: def remove_x(lst):
      return [char for char in lst if char != 'x']