Drop SVG_PAINTTYPE_* values that are never used (written)

Drop SVG_PAINTTYPE_UNKNOWN and SVG_PAINTTYPE_*_ICCCOLOR since there's
currently no code that sets anything to those values, and since they're
no longer part of a Web-facing API.

Review URL: https://codereview.chromium.org/545033003

git-svn-id: svn://svn.chromium.org/blink/trunk@182066 bbb929c8-8fbe-4397-9dbb-9b2b20218538