geolocate: first pass of code review and minor fixes (#359)

* doc(geolocate): minor cleanup

* more minor cleanups of geolocate

* remove disabled test and see whether now it works

internal/engine/model/model.go

@@ -1,7 +1,9 @@
 // Package model defines shared data structures and interfaces.
 package model
 
+import "github.com/ooni/probe-cli/v3/internal/engine/geolocate"
+
 const (
 	// DefaultProbeIP is the default probe IP.
-	DefaultProbeIP = "127.0.0.1"
+	DefaultProbeIP = geolocate.DefaultProbeIP
 )