compositor: migrate to stable viewporter.xml

Migrate from wl_scaler to wp_viewporter extension. The viewporter.xml
file is provided by wayland-protocols.

This stops Weston from advertising wl_scaler, and advertises
wp_viewporter instead.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
[Pekka: fix wayland-protocols requirement]
diff --git a/Makefile.am b/Makefile.am
index d1d2178..67c8f4b 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -130,8 +130,8 @@
 	protocol/input-method-unstable-v1-server-protocol.h		\
 	protocol/presentation-time-protocol.c		\
 	protocol/presentation-time-server-protocol.h	\
-	protocol/scaler-protocol.c			\
-	protocol/scaler-server-protocol.h		\
+	protocol/viewporter-protocol.c			\
+	protocol/viewporter-server-protocol.h		\
 	protocol/linux-dmabuf-unstable-v1-protocol.c	\
 	protocol/linux-dmabuf-unstable-v1-server-protocol.h