input: Write a function to remove a character at a specific index in a string.
  assert remove_character('Hello World!', 5) == 'HelloWorld!'
  assert remove_character('Python', 0) == 'ython'
  assert remove_character('Remove', 3) == 'Remve'
output: def remove_character(s: str, index: int) -> str:
      return s[:index] + s[index+1:]