Users.Delete does not soft-delete survey_responses table data

Created by: slimsag

This is an unintentional bug; when Users.Delete is called it is not soft-deleting data from the survey_responses table.

See this function:

https://sourcegraph.sgdev.org/github.com/sourcegraph/sourcegraph@9f467018d92c6e2b046f9950015eddb592da7e88/-/blob/cmd/frontend/db/users.go#L356:17