Remove setShouldDoFullPaintInvalidation from RenderBox::invalidatePaintIfNeeded()

The removed code forces full paint invalidation if the RenderBox did
position-movement only layout. This is unnecessary because we'll catch
the case and invalidate if needed if we find the box's
positionFromPaintInvalidationBacking or paintInvalidationRect changes.

TEST=existing tests

Review URL: https://codereview.chromium.org/622193002

git-svn-id: svn://svn.chromium.org/blink/trunk@183210 bbb929c8-8fbe-4397-9dbb-9b2b20218538