Revert "[Runtime Model] Packaging the XPK package generator in Linux & Windows"

We've never officially shipped any Windows or Linux archives, so this
target is not really serving any purpose.

This reverts commit 0b649e3b21882fe3b61afa8a4f46e6f54f51f144.
Merge pull request #1900 from rakuco/no-xpk-generator-target

Revert "[Runtime Model] Packaging the XPK package generator in Linux & Windows"