Deprecate ImagePalette size parameter

[radarhere]

Resolves #5636

The size parameter was originally added in #537. Before #5552, it was there to override a default length check.

Pillow/src/PIL/ImagePalette.py

Lines 45 to 48 in 10615a7

	if (size == 0 and len(self.mode) * 256 != len(self.palette)) or (
	size != 0 and size != len(self.palette)
	):
	raise ValueError("wrong palette size")

Afterwards though, the default length check was gone, so size is now just adding an arbitrary constraint on the user - if provided, it throws an error if palette parameter is not the length of the size parmeter.

Pillow/src/PIL/ImagePalette.py

Lines 43 to 44 in 3462b5f

	if size != 0 and size != len(self.palette):
	raise ValueError("wrong palette size")