Remove harmful default command to execute

modules/payloads/singles/php/exec.rb

@@ -26,7 +26,7 @@ module MetasploitModule
       ))
     register_options(
       [
-        OptString.new('CMD', [ true, "The command string to execute", 'echo "toor::0:0:::/bin/bash">/etc/passwd' ]),
+        OptString.new('CMD', [ true, "The command string to execute" ]),
       ])
   end