Switch to toybox echo(1).

Test: treehugger
Change-Id: Ie40cce5113f4b9bd17ec28c572952aacf1057804
diff --git a/ui/build/paths/config.go b/ui/build/paths/config.go
index 349dd25..0f36fba 100644
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -82,7 +82,6 @@
 	"date":      Allowed,
 	"dd":        Allowed,
 	"diff":      Allowed,
-	"echo":      Allowed,
 	"egrep":     Allowed,
 	"expr":      Allowed,
 	"find":      Allowed,
@@ -158,6 +157,7 @@
 	"cut":      Toybox,
 	"dirname":  Toybox,
 	"du":       Toybox,
+	"echo":     Toybox,
 	"env":      Toybox,
 	"head":     Toybox,
 	"id":       Toybox,