# What this PR does
- `AlertGroupPostMortem` has no references in the codebase.. I stumbled
across it while working on https://github.com/grafana/oncall/pull/5224
and decided to just remove it
- Removing old Slack channel related `VARCHAR` columns; these were
refactored to foreign key references to `slack_slackchannel` table in
following PRs:
- https://github.com/grafana/oncall/pull/5224
- https://github.com/grafana/oncall/pull/5199
- https://github.com/grafana/oncall/pull/5191
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
show up in the autogenerated release notes.
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