PR #109872 - sql: hide deprecated session vars from introspection

[cockroach-teamcity]

Exalate commented:

Related PR: cockroachdb/cockroach#109872
Commit: cockroachdb/cockroach@b70a34f
Epic: CRDB-28893
Fixes: CRDB-31127

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Release note (sql change): The deprecated session variable
idle_in_session_timeout is now hidden from introspection. (It has
been known as idle_session_timeout for a while already.)

Jira Issue: DOC-8729