[SPARK-3518] Remove wasted statement in JsonProtocol

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #2380 from sarutak/SPARK-3518 and squashes the following commits:

8a1464e [Kousuke Saruta] Replaced a variable with simple field reference
c660fbc [Kousuke Saruta] Removed useless statement in JsonProtocol.scala
[SPARK-2714] DAGScheduler logs jobid when runJob finishes

DAGScheduler logs jobid when runJob finishes

Author: yantangzhai <tyz0303@163.com>

Closes #1617 from YanTangZhai/SPARK-2714 and squashes the following commits:

0a0243f [yantangzhai] [SPARK-2714] DAGScheduler logs jobid when runJob finishes
fbb1150 [yantangzhai] [SPARK-2714] DAGScheduler logs jobid when runJob finishes
7aec2a9 [yantangzhai] [SPARK-2714] DAGScheduler logs jobid when runJob finishes
fb42f0f [yantangzhai] [SPARK-2714] DAGScheduler logs jobid when runJob finishes
090d908 [yantangzhai] [SPARK-2714] DAGScheduler logs jobid when runJob finishes