Switch to toybox ls(1).

Test: treehugger
Change-Id: I7abb1f657e02ccf2eaaff465adfb28114f66875e
diff --git a/ui/build/paths/config.go b/ui/build/paths/config.go
index 87f1e4e..4dc62b8 100644
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -95,7 +95,6 @@
 	"jar":       Allowed,
 	"java":      Allowed,
 	"javap":     Allowed,
-	"ls":        Allowed,
 	"lsof":      Allowed,
 	"m4":        Allowed,
 	"md5sum":    Allowed,
@@ -161,6 +160,7 @@
 	"head":     Toybox,
 	"id":       Toybox,
 	"ln":       Toybox,
+	"ls":       Toybox,
 	"mkdir":    Toybox,
 	"od":       Toybox,
 	"paste":    Toybox,