v8.5: remove VictoriaMetrics guide (#21538)

Author: lilin90

maintain-tidb-using-tiup.md

@@ -283,7 +283,7 @@ The destroy operation stops the services and clears the data directory and deplo
 tiup cluster destroy ${cluster-name}
 ```
 
-## Switch from Prometheus to VictoriaMetrics
+<!-- ## Switch from Prometheus to VictoriaMetrics
 
 In large-scale clusters, Prometheus might encounter performance bottlenecks when handling a large number of instances. Starting from TiUP v1.16.3, TiUP supports switching the monitoring component from Prometheus to VictoriaMetrics (VM) to provide better scalability, higher performance, and lower resource consumption.
 
@@ -433,3 +433,4 @@ After confirming that the old metrics have expired, you can perform the followin
     ```bash
     rm -rf /tidb-data/prometheus-8249
     ```
+-->