Simplify palette code

[radarhere]

As a consequence of #9985, data no longer needs to be converted to bytes here.

Pillow/src/PIL/Image.py

Lines 2170 to 2172 in 7e57b6c

	if not isinstance(data, bytes):
	data = bytes(data)
	palette = ImagePalette.raw(rawmode, data)

Before #9985, this change would have caused test failures from load()

Pillow/src/PIL/Image.py

Lines 989 to 990 in 7e57b6c

	mode, arr = self.palette.getdata()
	self.im.putpalette(self.palette.mode, mode, arr)

But no longer.

Also, given that the default ImagePalette mode is RGB, this is unnecessary.

Pillow/src/PIL/Image.py

Lines 2179 to 2180 in 7e57b6c

	else:
	self.palette.mode = "RGB"