Cleaned up the virtual overloads in long lived executor.
Cleaned up the virtual overloads in long lived executor.

This change removes the unused methods that won't be needed
after moving to the v1 API. It also renames `launchTask` to `launch`.
This review mainly eases reviewing later in the chain and should not
be committed on its own.

Review: https://reviews.apache.org/r/45797/

kaysoky/mesos,Gilbert88/mesos,chhsia0/mesos,jpeach/mesos,jpeach/mesos,kaysoky/mesos,abudnik/mesos,zmalik/mesos,andschwa/mesos,chhsia0/mesos,neilconway/mesos,abudnik/mesos,abudnik/mesos,craimbert/mesos,yuquanshan/customizedMesos,Aman-Jain-14/customizedMesos,asamerh4/mesos,kaysoky/mesos,verizonlabs/mesos,kaysoky/mesos,Gilbert88/mesos,zmalik/mesos,Gilbert88/mesos,asamerh4/mesos,dforsyth/mesos,neilconway/mesos,verizonlabs/mesos,asamerh4/mesos,chhsia0/mesos,reneploetz/mesos,zmalik/mesos,abudnik/mesos,zmalik/mesos,neilconway/mesos,yuquanshan/customizedMesos,Gilbert88/mesos,kaysoky/mesos,gsantovena/mesos,Aman-Jain-14/customizedMesos,reneploetz/mesos,gsantovena/mesos,abudnik/mesos,jpeach/mesos,dforsyth/mesos,andschwa/mesos,jpeach/mesos,craimbert/mesos,gsantovena/mesos,yuquanshan/customizedMesos,craimbert/mesos,reneploetz/mesos,Aman-Jain-14/customizedMesos,verizonlabs/mesos,andschwa/mesos,chhsia0/mesos,yuquanshan/customizedMesos,asamerh4/mesos,dforsyth/mesos,jpeach/mesos,zmalik/mesos,neilconway/mesos,verizonlabs/mesos,chhsia0/mesos,yuquanshan/customizedMesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,kaysoky/mesos,reneploetz/mesos,yuquanshan/customizedMesos,kaysoky/mesos,Aman-Jain-14/customizedMesos,asamerh4/mesos,craimbert/mesos,chhsia0/mesos,dforsyth/mesos,reneploetz/mesos,dforsyth/mesos,neilconway/mesos,verizonlabs/mesos,Gilbert88/mesos,jpeach/mesos,zmalik/mesos,gsantovena/mesos,dforsyth/mesos,Gilbert88/mesos,chhsia0/mesos,neilconway/mesos,gsantovena/mesos,andschwa/mesos,reneploetz/mesos,jpeach/mesos,neilconway/mesos,asamerh4/mesos,Gilbert88/mesos,Aman-Jain-14/customizedMesos,gsantovena/mesos,andschwa/mesos,andschwa/mesos,craimbert/mesos,abudnik/mesos,reneploetz/mesos,verizonlabs/mesos,abudnik/mesos,verizonlabs/mesos,andschwa/mesos,gsantovena/mesos,dforsyth/mesos,zmalik/mesos,asamerh4/mesos,Aman-Jain-14/customizedMesos,craimbert/mesos,craimbert/mesos