remove ineffective "Slack webhook" config action and settings schema property
Created by: sqs
a00f2fc02a83c4e8710d4dcf696b5b86e7105172 moved saved searches to the database and made Slack webhooks a per-saved-search option. The notifications.slack
setting is no longer effective (evidence: there were no Go references to the field).
Also removes the config action that set this property.