Switch to toybox which(1).

Test: treehugger
Change-Id: Ic14692b90c2b1246c1c8f72d00d6e0a5223aaf70
diff --git a/ui/build/paths/config.go b/ui/build/paths/config.go
index 305a8f4..b50748b 100644
--- a/ui/build/paths/config.go
+++ b/ui/build/paths/config.go
@@ -109,7 +109,6 @@
 	"timeout":   Allowed,
 	"tr":        Allowed,
 	"unzip":     Allowed,
-	"which":     Allowed,
 	"xz":        Allowed,
 	"zip":       Allowed,
 	"zipinfo":   Allowed,
@@ -175,6 +174,7 @@
 	"unix2dos":  Toybox,
 	"wc":        Toybox,
 	"whoami":    Toybox,
+	"which":     Toybox,
 	"xargs":     Toybox,
 	"xxd":       Toybox,
 }