issue-620: windows dll patching: fixed delete of old stub code

After code for issue 359 was applied PreamblePatcher started using
it's own code to manage memory of stub code fragments. It's not using
new[] anymore. And it automatically frees stub code memory on
Unpatch.

Clearly, author of that code forgot to remote that no more needed
delete call. With that delete call we end up trying to free memory
that was never allocated with any of known allocators and crash.