Remove unused geometry map from RenderLayer::updateLayerPositionsAfterScroll

No one uses this geometry map. We shouldn't pay the cost of maintaining it.

BUG=382770

Review URL: https://codereview.chromium.org/321223003

git-svn-id: svn://svn.chromium.org/blink/trunk@175924 bbb929c8-8fbe-4397-9dbb-9b2b20218538