PNG output has cICP and gAMA chunks

[Simon]

Summary of the bug:
How to reproduce:

% ffmpeg -y -f rawvideo -color_primaries bt709 -color_trc bt709 -colorspace bt709 -pix_fmt yuv422p16be -s 3840x2160 -i testcard.16 -vf scale=in_range=limited:out_range=limited -f image2 TestCard.png
ffmpeg version 6.1.1
  built with Apple clang version 15.0.0 (clang-1500.1.0.2.5)

Produces a PNG file with a correct cICP chunk and a gAMA chunk with a value of 0.510.
However, the PNG working draft states:
When the cICP chunk is present, decoders that recognize it SHALL ignore the following chunks:

iCCP
gAMA
cHRM
sRGB

So the gAMA chunk is not required and could cause issues.

[Balling]

Duplicate of my #10000. You are wrong fallback is required for cICP chunk.