sql: remove 'per app' references in sql stats fingerprint cluster seting

[jseldess]

Jesse Seldess (jseldess) commented:

PR: cockroachdb/cockroach#65902

From release notes:

The total number of statement/transaction fingerprints stored in-memory can now be limited using the [cluster settings](../v21.2/cluster-settings.html] sql.metrics.max_mem_stmt_fingerprints and sql.metrics.max_mem_txn_fingerprints. [#65902][#65902) {% comment %}doc{% endcomment %}

Jira Issue: DOC-1396