flaky test: rebalancer/stress_add_remove_several_rs.test

[Serpentian]

The test hangs on the following line:

rebalancer/stress_add_remove_several_rs.test.l> vinyl           Test timeout of 110 secs reached	[ fail ]

Test failed! Result content mismatch:
--- rebalancer/stress_add_remove_several_rs.result	Thu Mar 23 14:16:16 2023
+++ /home/runner/work/vshard/vshard/test/var/rejects/rebalancer/stress_add_remove_several_rs.reject	Thu Mar 23 14:20:43 2023
@@ -176,393 +176,3 @@
 ---
 ...
 wait_rebalancer_state('Rebalance routes are sent', test_run)
----
-...
--- Now, add a second replicaset.
-test_run:switch('default')
----
-- true
-...
-test_run:create_cluster(REPLICASET_4, 'rebalancer')

Reproduced on 2.7