Shrink RenderLayerCompositor by 5% by removing unused code

Remove has3DContent, layerHas3DContent
The last vestiges of these functions were removed with
https://src.chromium.org/viewvc/blink?revision=167695&view=revision
when Abarth removed isSoftwareRenderable.

Remove computeFixedViewportConstraints, computeStickyViewportConstraints
Jamesr removed the last callers in
https://src.chromium.org/viewvc/blink?view=rev&revision=147653

Remove clearMappingForAllRenderLayers, clearMappingForRenderLayerIncludingDescendants
These functions were added (under a different name) by Simon Fraser in
http://trac.webkit.org/changeset/90484. Jamesr removed the caller
in https://codereview.chromium.org/13818029.

Remove setCompositingParent, removeCompositedChildren
This code predates written history and possibly humankind.

Remove updateLayerTreeGeometry
Abarth removed the implementation but left the function definition in
https://src.chromium.org/viewvc/blink?view=rev&revision=168244

Remove updateGraphicsLayersMappedToRenderLayer
Abarth removed the implementation but left the function definition in
https://src.chromium.org/viewvc/blink?view=rev&revision=167697

Remove hasAnyAdditionalCompositedLayers
Shawn Singh removed the implementation but left the function definition
in https://src.chromium.org/viewvc/blink?view=rev&revision=163720

Review URL: https://codereview.chromium.org/209703002

git-svn-id: svn://svn.chromium.org/blink/trunk@169866 bbb929c8-8fbe-4397-9dbb-9b2b20218538