Revert "Add capability sets to the event system. Contains code from Duncan Coutts."

Revert "Add capability sets to the event system. Contains code from Duncan Coutts."

This reverts commit 58532eb46041aec8d4cbb48b054cb5b001edb43c.
Turns out it didn't work on Windows and it'll need some non-trivial changes
to make it work on Windows. We'll get it in later once that's sorted out.