input: Write a function to remove an element from an array at a specified index.
  assert remove([1, 2, 3, 4, 5], 2) == [1, 2, 4, 5]
  assert remove([10, 20, 30, 40, 50], 0) == [20, 30, 40, 50]
  assert remove([100, 200, 300, 400], 3) == [100, 200, 300]
output: def remove(arr, index):
      return arr[:index] + arr[index + 1:]