relay/api: close obsolete buffers when reconnecting to the remote

This closes all buffers that exist locally but not on the remote any more,
after reconnecting to the remote.

tests/unit/plugins/relay/api/remote/test-relay-remote-event.cpp

@@ -185,6 +185,16 @@ TEST(RelayRemoteEvent, RemoveLocalVarCb)
     /* TODO: write tests */
 }
 
+/*
+ * Tests functions:
+ *   relay_remote_event_initial_sync_buffers
+ */
+
+TEST(RelayRemoteEvent, InitialSyncBuffers)
+{
+    /* TODO: write tests */
+}
+
 /*
  * Tests functions:
  *   relay_remote_event_cb_buffer