input: Write a python function to remove the nth index character from a string.
  assert remove_nth_index("hello", 1) == "hllo"
  assert remove_nth_index("world", 3) == "wold"
  assert remove_nth_index("python", 0) == "ython"
  assert remove_nth_index("example", 6) == "exampl"
output: def remove_nth_index(s, n):
      return s[:n] + s[n+1:]