The kill above is sometimes successful and sometimes already too late.
The PING in pysnc wrong offset test got rejected by bgsaveerr because
lastbgsave_status is C_ERR.
In theory, using diskless can avoid PING being affected, because when
the replica is dropped, we will kill the child with SIGUSR1, and this
will not affect lastbgsave_status.
Anyway, this kill is not particularly needed here, dropping the kill
is the best one, since we do have the waitForBgsave, so just let it
take care of the bgsave. No need for fast termination.
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