deleteSeam = (img, seam, { w }) => {
  seam.forEach(({ x: seamX, y: seamY }) => {
    for (let x = seamX; x < (w - 1); x += 1) {
      const nextPixel = getPixel(img, { x: x + 1, y: seamY });
      setPixel(img, { x, y: seamY }, nextPixel);
    }
  });
}
Deletes the seam from the image data.
We delete the pixel in each row and then shift the rest of the row pixels to the left.
@param {ImageData} img
@param {Seam} seam
@param {ImageSize} size