Use more general ooni/probe-engine API (#67)

No functional change, just importing less stuff and meddling
much less with the internals of ooni/probe-engine.

internal/enginex/enginex.go

@@ -2,10 +2,7 @@
 package enginex
 
 import (
-	"encoding/json"
-
 	"github.com/apex/log"
-	"github.com/ooni/probe-engine/model"
 )
 
 // Logger is the logger used by the engine.
@@ -13,30 +10,6 @@ var Logger = log.WithFields(log.Fields{
 	"type": "engine",
 })
 
-// MakeGenericTestKeys casts the m.TestKeys to a map[string]interface{}.
-//
-// Ideally, all tests should have a clear Go structure, well defined, that
-// will be stored in m.TestKeys as an interface. This is not already the
-// case and it's just valid for tests written in Go. Until all tests will
-// be written in Go, we'll keep this glue here to make sure we convert from
-// the engine format to the cli format.
-//
-// This function will first attempt to cast directly to map[string]interface{},
-// which is possible for MK tests, and then use JSON serialization and
-// de-serialization only if that's required.
-func MakeGenericTestKeys(m model.Measurement) (map[string]interface{}, error) {
-	if result, ok := m.TestKeys.(map[string]interface{}); ok {
-		return result, nil
-	}
-	data, err := json.Marshal(m.TestKeys)
-	if err != nil {
-		return nil, err
-	}
-	var result map[string]interface{}
-	err = json.Unmarshal(data, &result)
-	return result, err
-}
-
 // LocationProvider is an interface that returns the current location. The
 // github.com/ooni/probe-engine/session.Session implements it.
 type LocationProvider interface {