Update slack-map.md (#1892)
Update slack-map.md (#1892)

Removed all excessive activity channels to consolidate chatter onto #gardening-general, #gardening-ineedhelp, and #gardening-training

Co-authored-by: Dave Dorbin <3a983b921291999521a653180c5b82ccd2c36700@google.com>
spinnaker/spinnaker.github.io,spinnaker/spinnaker.github.io,spinnaker/spinnaker.github.io