Remove some dead scrolling paths and unused params

didScrollRect turns out to be useless as do some scroll delta params,
so I've deleted them.

Note this patch depends on: https://codereview.chromium.org/347053005

BUG=None

Review URL: https://codereview.chromium.org/348193002

git-svn-id: svn://svn.chromium.org/blink/trunk@176802 bbb929c8-8fbe-4397-9dbb-9b2b20218538