Add a target_ops parameter to the to_kill method in struct target_ops.

    Add a target_ops parameter to the to_kill method in struct target_ops.

        * target.h (struct target_ops): Add a "target_ops *" parameter to
        method to_kill.
        (target_kill): Remove macro. Add declaration.
        * target.c (debug_to_kill): Delete, no longer necessary.
        (target_kill): New function.
        (update_current_target):  Stop inheriting the to_kill method.
        Do not de_fault it to no_process either.
        (setup_target_debug): Do not set current_target.to_kill.
        * gnu-nat.c, go32-nat.c, hpux-thread.c, inf-ptrace.c, inf-ttrace.c,
        linux-nat.c, monitor.c, nto-procfs.c, procfs.c, remote-m32r-sdi.c,
        remote-mips.c, remote-sim.c, remote.c, windows-nat.c: Update
        accordingly.