PlayOnLinux is in both Portage and Entropy but, judging by the lack of response to your question, it seems no SL forum members use it.
Have you looked on the PlayOnLinux site? The on-line manual tells you how to remove an application:
PlayOnLinux User Manual.
I also googled and found the following thread in the Ubuntu forums, which may be of help if, for some reason, you are unable to remove the installed game using the PlayOnLinux application as described in the PlayOnLinux manual:
uninstalling in playonlinux