compositor: Don't export weston_compositor_repick()

Picking is tied into the repaint loop and shouldn't happen outside
weston_output_repaint(), so don't export weston_compositor_repick().
diff --git a/src/compositor.c b/src/compositor.c
index 053dfd1..c93da34 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -614,7 +614,7 @@
 					         &seat->pointer->grab->y);
 }
 
-WL_EXPORT void
+static void
 weston_compositor_repick(struct weston_compositor *compositor)
 {
 	struct weston_seat *seat;