input: Write a function to remove all occurrences of a specific character from a string.
  assert remove_char('hello world', 'o') == 'hell wrld'
  assert remove_char('mississippi', 's') == 'miippi'
  assert remove_char('python programming', 'g') == 'python prorammin'
output: def remove_char(s, char):
      return s.replace(char, '')