Ok, this cannot be removed, that I know of at the moment, you can however purge
kirigami2-dev and libkf5kirigami2-doc if installed.
Kirigami in a QML based UI framework at the core of some KDE applications, which will become more and more central as more and more QML based applications are made.
Plasma 5.8 will depend from Kirigami 1.1, so if you are planning to write a Kirigami-based application, it will work by default and nicely integrate in the Plasma 5.8 desktop.
Plasma 5.8 also has a new big user for Kirigami 1.1, that is Discover: the application to search and install for new software, has a brand new user interface, based upon Kirigami.
But next time you have a problem with your system, please mention right away that you are using a encrypted system