[PATCH weston] compositor: rebuild the global list if we've removed a surface from it

[Rob Bradford]

Hi Pekka,

You raise a good point. I don't think the increase in complexity is
worth it - we have good way to construct a surface list from the
layers (and we do it at the start of every frame) anyway: I think it's
nice that the management of this cache is really encapsulated in a
single place.

Rob