No need to set FACELET_CONTEXT_KEY in DefaultFaceletContext constructor

In MYFACES-3246 the following constructor was updated:

DefaultFaceletContext(FacesContext faces, AbstractFacelet facelet, FaceletCompositionContext mctx)

It no longer does the following:

//Set FACELET_CONTEXT_KEY on FacesContext attribute map, to
//reflect the current facelet context instance
faces.getAttributes().put(FaceletContext.FACELET_CONTEXT_KEY, this);

Setting the FACELET_CONTEXT_KEY is now done where ever the DefaultFaceletContext is created for instance in DefaultFacelet.

DefaultFaceletContext ctxWrapper = new DefaultFaceletContext((DefaultFaceletContext)ctx, this, false);
ctx.getFacesContext().getAttributes().put(FaceletContext.FACELET_CONTEXT_KEY, ctxWrapper);

However, the other constructor which is actually being called above still sets the FACELET_CONTEXT_KEY and so it is set in the constructor and then set again directly after creation.

//Update FACELET_CONTEXT_KEY on FacesContext attribute map, to
//reflect the current facelet context instance
ctx.getFacesContext().getAttributes().put(FaceletContext.FACELET_CONTEXT_KEY, this);

I think this was just an oversight when fixing this bug. But I think we should clean this up and I'll provide the trivial patch that can be applied.