protocol: move sub-surfaces to Wayland

protocol: move sub-surfaces to Wayland

This reverts commit 2396aec6842c709a714f3825dbad9fd88478f2e6.

This exact version of the sub-surface protocol has been copied into
Wayland core. Therefore it must be removed from here to avoid build
conflicts and useless duplication.

No other changes to sub-surface protocol consumers are needed, the
identical API is now offered by libwayland-client and libwayland-server.

The commit adding sub-surfaces to Wayland is:
Author: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

    protocol: add sub-surfaces to the core

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>