Fix Vm#supports_terminate? checking EMS#vm_destroy

We removed the redundant EMS#vm_destroy methods which just called
VM#raw_destroy for all providers except VMware.  The supports_feature
block however was still checking if the EMS respond_to?(:vm_destroy)
rather than checking if the vm object responds to it.

app/models/vm_or_template/operations.rb

@@ -142,7 +142,7 @@ def validate_vm_control_shelve_offload_action
 
     supports :terminate do
       msg = unsupported_reason(:control) unless supports_control?
-      msg ||= _("Provider doesn't support vm_destroy") unless ext_management_system.respond_to?(:vm_destroy)
+      msg ||= _("Provider doesn't support vm_destroy") unless respond_to?(:vm_destroy)
       unsupported_reason_add(:terminate, msg) if msg
     end
   end