chore: Remove model hub

[MikhailKardash]

Ticket

https://hpe-aiatscale.atlassian.net/browse/MD-461

Description

Remove model_hub library and subdirectory from determined

Test Plan

No testing required

Checklist

• [ ] Changes have been manually QA'd
• [ ] New features have been approved by the corresponding PM
• [ ] User-facing API changes have the "User-facing API Change" label
• [ ] Release notes have been added as a separate file under docs/release-notes/ See Release Note for details.
• [ ] Licenses have been included for new code which was copied and/or modified from any external code