[3.11] gh-106498: Revert incorrect colorsys.rgb_to_hls change (GH-106627) (#106633)

gh-106498: Revert incorrect colorsys.rgb_to_hls change (GH-106627)

gh-86618 assumed a-b-c = a-(b+c) = a-d where d = b+d.
For floats 2.0, 1.0, and 0.9999999999999999, this assumption
is false.  The net change of 1.1102230246251565e-16 to 0.0
results in division by 0.  Revert the replacement.  Add test.
(cherry picked from commit a2d54d4e8ab12f967a220be88bde8ac8227c5ab3)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>