pktgen: remove unused variable

pktgen_thread_worker() no longer needs wait variable, delete it.

Fixes: ef87979c ("pktgen: better scheduler friendliness")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>