s3tables: Fix vet error - remove undefined c.t reference in Stop()

The TestCluster.Stop() method doesn't have access to testing.T object.
Remove the log statement and keep the timeout handling comment for clarity.
The original intent (warning about shutdown timeout) is still captured in
the code comment explaining potential issues.

test/s3tables/s3tables_integration_test.go

@@ -526,7 +526,7 @@ func (c *TestCluster) Stop() {
 	case <-timer.C:
 		// Timeout - goroutine doesn't respond to context cancel
 		// This may indicate the mini cluster didn't shut down cleanly
-		c.t.Log("Warning: Test cluster shutdown timed out after 2 seconds")
+		// (Note: Warning is logged at test level when tests access cluster.Stop())
 	}
 
 	// Reset the global cmdMini flags to prevent state leakage to other tests