Nothing in-tree uses this function, and its functionality has been
replaced with the weston-output-capture protocol extension which is
implemented in libweston core.

Users of this function should migrate to
weston_compositor_add_screenshot_authority() and replace custom
screenshooting protocols with weston-output-capture.xml installed by
libweston.

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