Delete malfunctioning Codeplex casks, fixes #6618

pcsxr, wabbitemu and winxound casks were using a URL that lasts only for
24 hours. These casks never worked. There is no way to get a permanent
URL from Codeplex, and that means there is no way to fix those casks.
Merge pull request #6630 from yegortimoschenko/avoid-codeplex

Delete malfunctioning Codeplex casks, fixes #6618