Remove scrollbars from more pageScaleFactor tests.

These scrollbars are brittle on some platforms to the change in
https://codereview.chromium.org/138013006

BUG=341145
TBR=abarth
NOTRY=true

Review URL: https://codereview.chromium.org/148853006

git-svn-id: svn://svn.chromium.org/blink/trunk@166760 bbb929c8-8fbe-4397-9dbb-9b2b20218538