Remove check for UUID in the valid session check

This is causing sessions to fail because meterpreter isn't doing the
right thing. I have another fix in the works which will properly solve
this, but in the short term the best way of solving the problem is to
remove this line.

lib/msf/base/sessions/meterpreter.rb

@@ -307,7 +307,9 @@ class Meterpreter < Rex::Post::Meterpreter::Client
 
     begin
       self.machine_id = self.core.machine_id(timeout)
-      self.payload_uuid ||= self.core.uuid(timeout)
+      # This is causing breakages thanks to Meterpeter not doing what it should
+      # be doing with the uuid.
+      #self.payload_uuid ||= self.core.uuid(timeout)
 
       return true
     rescue ::Rex::Post::Meterpreter::RequestError