DISPATCH-2356: Remove integer offered capability values from test_50_extension_capabilities

The AMQP standard requires that there be symbol array or a single symbol (#985)

(cherry picked from commit 2a85d02202e6401b9e2df5dbb2e1808386a8cc1a)
diff --git a/tests/system_tests_one_router.py b/tests/system_tests_one_router.py
index 25ec109..287cb9d 100644
--- a/tests/system_tests_one_router.py
+++ b/tests/system_tests_one_router.py
@@ -734,7 +734,6 @@
         """
         client_caps = [symbol("single"),
                        ["A", "B", "C"],
-                       [9, 10, 11],
                        [],
                        None]