client: Make --nocheckstate the default for disconnect
client: Make --nocheckstate the default for disconnect

- Make --nocheckstate the default for "isr disconnect"; the user can request
otherwise with --checkstate.  Making --checkstate the default is
unnecessarily paranoid.

- Eliminate --nocheckstate flag, since it is now unused

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr