fixes the following issues:
pkg/controller/acmeorders/util.go:84:6 deadcode `hashChallenge` is unused
pkg/controller/certificaterequests/approver/approver.go:72:14 staticcheck SA4021: x = append(y) is equivalent to x = y
pkg/controller/certificaterequests/vault/vault_test.go:535:21 errcheck Error return value of `controller.Register` is not checked
pkg/controller/certificates/trigger/policies/policies.go:121:26 gosimple S1039: unnecessary use of fmt.Sprintf
pkg/controller/clusterissuers/sync_test.go:55:12 errcheck Error return value of `c.Register` is not checked
pkg/controller/ingress-shim/sync.go:301:2 gosimple S1005: unnecessary assignment to the blank identifier
Signed-off-by: Ashley Davis <ashley.davis@jetstack.io>
c67c2c4f47