tests: remove color-manager test

This is very trivial test, which does not skip correctly when built with
color-management-lcms=false. It fails instead.

Since alpha-blending test already covers everything that color-manager
test did, remove color-manager test.

My editor eliminated a stray whitespace, too.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>