gossip,kvserver,sql: remove the last vestiges of the systemconfig gossip in 22.2.

[ajwerner]

Is your feature request related to a problem? Please describe.
In 22.1, with #76279, we removed the functionality which gossips the system config span. We keep around pieces of it for the mixed version state. This issue is a placeholder to remove the now deprecated code in the 22.2 cycle.

Jira issue: CRDB-13197

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