CASSANDRA-21154 remove traces of sampling and auto training

[smiklosovic]

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The Cassandra Jira

[smiklosovic]

to shut up idea code style

[smiklosovic]

also

logger.info("Started dictionary training for {}.{}", keyspaceName, tableName);

below is suspicious. I would not log anything, actually.

[yifan-c]

Agreed on the log message removal. Given that, the training is manual, the log message to indicate the start of the process is less useful.

[yifan-c]

Looks good overall. Thank you for tidying up the currently unused code in the dictionary compression domain!