[jmx-metrics] Copypasta/incorrect reference to Cassandra

[breedx-splk]

Component(s)

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What happened?

jvm.md here https://github.com/open-telemetry/opentelemetry-java-contrib/blob/main/jmx-metrics/docs/target-systems/jvm.md contains reference to Cassandra, which is inaccurate. I think it's just copypasta and can be edited.

Component version

trunk/main

Log output

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Additional context

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