remove abandoned skii.rb

* Original homepage (http://www.awesome-studio.tk/) taken over by squatters.
  I get various redirections, including one which generated a malware warning.
* The `url` points to an anonymous cloud.app user.
* The macupdate page referenced as `homepage` points to the same cloud.app
  download.

It seems that nobody is vouching for this binary.  Historical awesome-studio.tk
is also blocked from the Wayback Machine.  We have no information about the
provenance of this app, and should not include it.
Merge pull request #6570 from rolandwalker/remove_skii

remove abandoned skii.rb