Depth of a rendernode should be determined by the textures used and the
compositing colorstate requirements.
Colors influence the colorstate choice, so they indirectly influence the
depth, but they should not influence the depth directly.
Otherwise a single color in a border being rec2100-pq would make us
switch to 16bit float.
Also remove gdk_color_get_depth(), because it was only used here and
because again: Colors should not influence depth decisions.
Unless there is a very good reason to use memcpy(), don't use it.
Not using it makes the compiler not screw up and waste tons of CPU that
it could have not wasted.
Gets my framerate back from 1250 => 1750 and makes sysprof no longer
report ~40% of render time spent in gsk_gpu_colorize_op().