hush: kill some old unused fields; small code shrink

function                                             old     new   delta
builtin_exit                                          48      47      -1
checkjobs                                            351     335     -16
checkjobs_and_fg_shell                                60      35     -25
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(add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-42)             Total: -42 bytes

1 file changed