Remove a wrong FIXME comment for SVGCursorElement

BUG=357163
TBR=oilpan-reviews,haraken
NOTRY=true

Review URL: https://codereview.chromium.org/302763005

git-svn-id: svn://svn.chromium.org/blink/trunk@174916 bbb929c8-8fbe-4397-9dbb-9b2b20218538