tests/test_stasis_endpoints: Remove expected duplicate events

The cache_clear test was written to expect duplicate Stasis messages
sent from the technology endpoint to the all caching topic. This patch
fixes the test to no longer expect these duplicate messages.

ASTERISK-25137

Change-Id: I58075d70d6cdf42e792e0fb63ba624720bfce981

tests/test_stasis_endpoints.c

@@ -186,9 +186,10 @@ AST_TEST_DEFINE(cache_clear)
 
 	/* Note: there's a few messages between the creation and the clear.
 	 * Wait for all of them... */
-	message_index = stasis_message_sink_wait_for(sink, message_index + 4,
+	message_index = stasis_message_sink_wait_for(sink, message_index + 2,
 		cache_update, __func__, STASIS_SINK_DEFAULT_WAIT);
 	ast_test_validate(test, 0 <= message_index);
+
 	/* Now we should have a cache removal entry */
 	msg = sink->messages[message_index];
 	type = stasis_message_type(msg);