Rip out RenderLayerCompositor::m_needsToRecomputeCompositingRequirements

We've now cleaned up the compositing code sufficiently that we
don't need a separate dirty bit to track this state. Instead,
we can just use m_updateType to track this information, as we
do for all the other update types.

Most of the callers that explicitly set this dirty bit were
doing so redundantly because they were called during style
recalc or during layout, which already set strictly more
powerful dirty bits.

There were two cases where we actually needed the dirty bit,
but we can just use CompositingUpdateAfterCompositingInputChange
instead, which does essentially the same thing.

Review URL: https://codereview.chromium.org/312683002

git-svn-id: svn://svn.chromium.org/blink/trunk@175401 bbb929c8-8fbe-4397-9dbb-9b2b20218538