[demo pipelines] remove slack on success hook
Open to pushback on this. A few reasons here:
- The implementation includes hardcoded values from the Elementl dogfooding setup.
- This is a weakly-held opinion, but I think success hooks are kind of an anti-pattern. Any success hook can be written as a regular solid, and having two recommended ways of doing the same thing is awkward.
- What the hook is doing in this case is unrealistic. I don't think I would want a slack message every hour reporting that I pulled some data into an S3 table.
Test Plan: bk
Reviewed By: owen
Differential Revision: https://dagster.phacility.com/D9205