Remove references from the code to Jira Issues

[Taragolis]

Airflow codebase contains references to the https://issues.apache.org/jira/browse/ ISSUES:

• Some of them outdated or expect modifications into the Deprecated things, e.g. SubDags
• Some of them non-relevant (code changed, version of software upgrade)
• Some of them do not add any additional content.

In addition old Airflow Jira issues not-publicity available, and required request to grant this access.
So maybe it is a good time remove references to them?

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