Revert "monitoring: configure alert notifications from site config"

Created by: bobheadxi

Reverts sourcegraph/sourcegraph#11427

There seems to be some problems:

• sourcegraph/server is not properly handled (sourcegraph.sgdev.com makes a request to grafana-wrapper still and shows an error) - in general, I think opt-out cases needs a second pass
• on dot-com, configuration is getting in from somewhere that is causing the wrapper to look in the wrong place for Grafana - this is set by GRAFANA_PORT, but as far as I can know is not set by anywhere (notice 30070 instead of 3371, as well the more obscure last error that I'm not sure I understand) - this is putting Grafana in a crash loop

"t=2020-06-13T04:34:54+0000 lvl=crit msg="failed to initialize configuration" cmd=grafana-wrapper error="grafana not reachable: Get \"http://admin:***@127.0.0.1:tcp/10.55.253.135:30070/api/health\": context deadline exceeded (last error: Get \"http://admin:***@127.0.0.1:tcp/10.55.253.135:30070/api/health\": dial tcp: lookup 127.0.0.1:tcp: no such host)"

It might be best to punt this to the next release - will revisit next week to see if I can get this fixed up by branch cut