Removed unused declaration.
Removed unused declaration.

The declaration of this operator was not needed here. It was also
done in a surprising namespace as the 'Task' equality operator lives
in the 'mesos' namespace while this declaration was in
'mesos::internal'.

Review: https://reviews.apache.org/r/63494/

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