remove replacer

Created by: rvantonder

This PR removes replacer/codemod and all references I could find to it. It served its purpose :-) There are a lot of places that a service touches, so this is best-effort. I tried to be thorough, but it may very well break things if I missed something. This PR does not update deploy configurations for the replacer service (which should maybe be removed before merging this change).

Removes:

• cmd/replacer service
• replace: field in queries
• codemod references/GQL requests in web code
• GQL type and resolvers for codemod/codemod results
• removes replacer from Procfile and start/dev/ci scripts
• removes replacer from architecture docs
• removes replacer from monitoring

Checked the following still work:

• dev startup
• go build
• go tests

Will let CI check the rest.