Garbage-collect some no longer relevant patching (it does nothing these
days); these are not the changes being made, these are previous changes
being removed:

• Fix CTLFLAG_* values for SYSCTL_ADD_PROC() after FreeBSD src r273377
• Replace d_thread_t' (FreeBSD 4 support compat shim) with struct thread'

Reviewed by: grep(1), diff(1), sha1(1)