emul_native is only used for kernel threads which can't dump core, so

emul_native is only used for kernel threads which can't dump core, so
delete coredump_trad(), uvm_coredump(), cpu_coredump(), struct md_coredump,
and various #includes that are superfluous.

This leaves compat_linux processes without a coredump callback.  If that
ability is desired, someone should update it to use coredump_elf32() and
verify the results...

ok kettenis@