Remove unused and incorrect RenderStyle::initialTextEmphasisColor.

Initial -webkit-text-emphasis-color (correctly) uses
StyleColor::currentColor, like most of the other colors.

Also, initialTextEmphasisColor returns TextEmphasisFillFilled, which is not a Color.

Review URL: https://codereview.chromium.org/425763002

git-svn-id: svn://svn.chromium.org/blink/trunk@179046 bbb929c8-8fbe-4397-9dbb-9b2b20218538