Move //mojo/services/X/public/... to //mojo/services/X/... (part 4).

X = vanadium/security,
    view_manager,
    window_manager

(This is the last one, except for network, which is pulled from monet.)

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/1391243003 .
diff --git a/services/vanadium/security/principal_service.go b/services/vanadium/security/principal_service.go
index 26ebe66..6f31f5b 100644
--- a/services/vanadium/security/principal_service.go
+++ b/services/vanadium/security/principal_service.go
@@ -20,7 +20,7 @@
 	auth "mojo/services/authentication/interfaces/authentication"
 	network "mojo/services/network/public/interfaces/network_service"
 	"mojo/services/network/public/interfaces/url_loader"
-	vpkg "mojo/services/vanadium/security/public/interfaces/principal"
+	vpkg "mojo/services/vanadium/security/interfaces/principal"
 )
 
 //#include "mojo/public/c/system/types.h"