move subsurface-server-protocol.h include out of compositor.h

The subsurface-server-protocol.h header should not be included
by any headers that are part of the SDK since it is not exported.
Otherwise, SDK consumers will break during compilation.

Move this include from compositor.h to compositor.c.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=64537

Signed-off-by: U. Artie Eoff <ullysses.a.eoff@intel.com>
diff --git a/src/compositor.c b/src/compositor.c
index c1f90ca..c16bf0c 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -56,6 +56,7 @@
 
 #include <wayland-server.h>
 #include "compositor.h"
+#include "subsurface-server-protocol.h"
 #include "../shared/os-compatibility.h"
 #include "git-version.h"
 #include "version.h"