Fix an unnecessary cast calling elog in ExecHashJoinImpl

Hi,

While debugging the HashJoin codes, I noticed below codes in ExecHashJoinImpl():

elog(ERROR, "unrecognized hashjoin state: %d",
(int) node->hj_JoinState);

The type of hj_JoinState is already int, so the cast seems unnecessary.

So I remove it in the attached patch.