Remove the unreferenced DATA() macro. That leaves only GET_CURTHREAD_PTR()
which was added by cognet in 2012, so remove the no-longer-applicable
license stuff that referred to all the old contents, and put in a
standard 2-clause BSD license (to cover the 6 lines of useful code left
in here).
Remove #include <machine/asmacros.h> from files that don't need it.