User Guide: Remove bad G1 tuning advice

The "Managing Heap Memory" page provides some G1 tuning advice that is actually detrimental to performance. The whole section needs some work, but this passage, in particular, is wrong:

If you find the Apache Geode Resource Manager does not detect crossing the eviction or critical threshold quickly enough, it has been observed that its responsiveness is increased by reducing the default value of --J-XX:MaxGCPauseMillis=VALUE JVM parameter (which is 200). Be sure to take into account that this change also increases the amount of time spent in garbage collection.

Cause: This advice was originally intended only to maximize performance of a specific test case. It is NOT good advice for production systems.

https://geode.apache.org/docs/guide/114/managing/heap_use/heap_management.html

Short-term solution: delete the passage.
Long-term solution: Come up with some better ideas.