Remove unused class CSSArrayFunctionValue

The class CSSArrayFunctionValue was introduced a while back for custom
filters which have since been removed, so the class is now unused.

Review URL: https://codereview.chromium.org/472753002

git-svn-id: svn://svn.chromium.org/blink/trunk@180278 bbb929c8-8fbe-4397-9dbb-9b2b20218538