Revert "Merge "Remove ability to downgrade importance of existing channel." into oc-dr1-dev"

This reverts commit d691f1a200b4c1362219fceece7400dd38ef117e, reversing
changes made to d6a2ed194c474d1894a53636353760120c8a11d7.

Test: runtest systemui-notification
Fixes: 63920384
3 files changed