Removed an unused variable in a default executor test.
Removed an unused variable in a default executor test.

This patch removes an unused variable from
`DefaultExecutorTest.CommitSuicideOnKillTask`.

Review: https://reviews.apache.org/r/63522/

abudnik/mesos,kaysoky/mesos,jpeach/mesos,reneploetz/mesos,kaysoky/mesos,kaysoky/mesos,Gilbert88/mesos,Gilbert88/mesos,jpeach/mesos,gsantovena/mesos,abudnik/mesos,asamerh4/mesos,asamerh4/mesos,Gilbert88/mesos,gsantovena/mesos,andschwa/mesos,chhsia0/mesos,gsantovena/mesos,andschwa/mesos,reneploetz/mesos,andschwa/mesos,asamerh4/mesos,andschwa/mesos,Gilbert88/mesos,chhsia0/mesos,jpeach/mesos,dforsyth/mesos,abudnik/mesos,dforsyth/mesos,abudnik/mesos,kaysoky/mesos,abudnik/mesos,dforsyth/mesos,asamerh4/mesos,dforsyth/mesos,gsantovena/mesos,dforsyth/mesos,gsantovena/mesos,Gilbert88/mesos,asamerh4/mesos,abudnik/mesos,andschwa/mesos,jpeach/mesos,kaysoky/mesos,chhsia0/mesos,jpeach/mesos,reneploetz/mesos,Gilbert88/mesos,dforsyth/mesos,chhsia0/mesos,asamerh4/mesos,chhsia0/mesos,kaysoky/mesos,reneploetz/mesos,reneploetz/mesos,abudnik/mesos,jpeach/mesos,chhsia0/mesos,chhsia0/mesos,reneploetz/mesos,andschwa/mesos,reneploetz/mesos,andschwa/mesos,asamerh4/mesos,kaysoky/mesos,gsantovena/mesos,gsantovena/mesos,jpeach/mesos,Gilbert88/mesos,dforsyth/mesos