Revert "[SVG2] Allow leading and trailing whitespace in svg attributes using"

whitespace-length.html is timing out consistently on Webkit XP:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=fast/svg/whitespace-length.html

BUG=377503,339899
TBR=ed@opera.com

Review URL: https://codereview.chromium.org/319883002

git-svn-id: svn://svn.chromium.org/blink/trunk@175616 bbb929c8-8fbe-4397-9dbb-9b2b20218538