Removed unused capture of this.
Removed unused capture of this.

clang-5 has a warning about unused lambda captures in its -Wall set.
Removing this unused capture here to enable building with clang-5.

Review: https://reviews.apache.org/r/58795/

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