libweston: Migrate weston_environment_get_fd() to weston-launch header

This is private so it doesn't belong to public libweston API header.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

include/libweston/libweston.h

@@ -1949,9 +1949,6 @@ void
 weston_compositor_set_default_pointer_grab(struct weston_compositor *compositor,
 			const struct weston_pointer_grab_interface *interface);
 
-int
-weston_environment_get_fd(const char *env);
-
 struct weston_surface *
 weston_surface_create(struct weston_compositor *compositor);
 

libweston/weston-launch.h

@@ -46,4 +46,7 @@ struct weston_launcher_open {
 	char path[0];
 };
 
+int
+weston_environment_get_fd(const char *env);
+
 #endif