Remove SVGElementInstance includes, these are not
needed anymore after
https://codereview.chromium.org/268223003

BUG=313438

Review URL: https://codereview.chromium.org/309553009

git-svn-id: svn://svn.chromium.org/blink/trunk@175212 bbb929c8-8fbe-4397-9dbb-9b2b20218538