Switch to toybox readlink(1).

Test: treehugger
Change-Id: Ie1f6be5c2f273809a2691e506fc34c6840c942dd
diff --git a/ui/build/paths/config.go b/ui/build/paths/config.go
index 1afcf55..1b80ceb 100644
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -107,7 +107,6 @@
 	"python":    Allowed,
 	"python2.7": Allowed,
 	"python3":   Allowed,
-	"readlink":  Allowed,
 	"realpath":  Allowed,
 	"rm":        Allowed,
 	"rsync":     Allowed,
@@ -163,6 +162,7 @@
 	"od":       Toybox,
 	"paste":    Toybox,
 	"pwd":      Toybox,
+	"readlink": Toybox,
 	"rmdir":    Toybox,
 	"setsid":   Toybox,
 	"sleep":    Toybox,