Remove scheduler migration logic on next major version bump

[lmossman]

Some temporary logic was added to the airbyter ServerApp and the JobPersistence classes to support the migration from the old scheduler to the new temporal scheduler. See this PR for those changes: #12757

Once we perform another "major" version bump that requires users to upgrade to some intermediate version that includes these changes, we can then remove this logic from the next version of Airbyte that comes after that.

Acceptance Criteria:

• The migration logic and persistence methods introduced in the PR linked above are removed from the Airbyte codebase after the next "major" version bump

[benmoriceau]

We could use this version bump in order to:

• to have a version that contains airbytehq/airbyte-internal-issues#616 for sure.
• to remove the metadata code for the secrets that have been introduced in Migrate to a secret store by default #12516

[davinchia]

@benmoriceau @colesnodgrass if I'm poking around the job persistence class, do you mind if I grab this issue?

[benmoriceau]

@davinchia No, feel free to do it.