Switch to toybox ln(1).

Test: treehugger
Change-Id: Ia52e73e87a6c4648285d2340908013cd8528d221
diff --git a/ui/build/paths/config.go b/ui/build/paths/config.go
index e5e0821..87f1e4e 100644
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -95,7 +95,6 @@
 	"jar":       Allowed,
 	"java":      Allowed,
 	"javap":     Allowed,
-	"ln":        Allowed,
 	"ls":        Allowed,
 	"lsof":      Allowed,
 	"m4":        Allowed,
@@ -161,6 +160,7 @@
 	"expr":     Toybox,
 	"head":     Toybox,
 	"id":       Toybox,
+	"ln":       Toybox,
 	"mkdir":    Toybox,
 	"od":       Toybox,
 	"paste":    Toybox,