motif: State structure cleanup

motif: State structure cleanup

- We don't actually need to store the render task IDs in the
  state structure; the only thing we actually care about is to
  avoid multiple registration.  We can use two otherwise-unused
  bits of the render mask to track this.

- The window size tracking is no longer used, so these members
  are just a waste of space and can be removed.

- The remaining members can be rearranged to avoid padding.