input: Write a python function to remove all occurrences of a specified character from a string.
  assert remove_char('hello world', 'l') == 'heo word'
  assert remove_char('banana', 'a') == 'bnn'
  assert remove_char('mississippi', 's') == 'miiippi'
output: def remove_char(s: str, char: str) -> str:
      return s.replace(char, '')