Summary:
Non-runtime AutoFlags has never been used. The macro was removed almost 2 years back in 7db84bce339fb664c79774495589ca1781ca069b/D25569
This change cleans up all the code related to non-runtime AutoFlags.

**Upgrade/Downgrade safety: **
`promote_non_runtime_flags` field in `PromoteAutoFlagsRequestPB` has been removed. This was never used except for in tests and yb-admin, which have also been cleaned up.
Jira: DB-15211

Test Plan: Jenkins

Reviewers: asrivastava, xCluster

Reviewed By: asrivastava

Subscribers: yugaware, ybase, ycdcxcluster

Differential Revision: https://phorge.dev.yugabyte.com/D41745