Bug 1571758 - Drop scroll method from SpatialNode. r=gw
Bug 1571758 - Drop scroll method from SpatialNode. r=gw

It's not used for Gecko at all. And in the next commit we are going to have
multiple scroll offsets in a ScrollFrameInfo and encapsulate
ScrollFrameInfo.scroll_offset method so with this unused scroll function,
the next change will be quite messy.

Differential Revision: https://phabricator.services.mozilla.com/D133443

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/b13b738bc31b853dd2debba07b80dce8da4185ea

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender