Removal of contrib: GDR, Verbs and MPI

[Günhan Gülsoy]

Hi all,

I am slowly removing all of contrib, piece by piece.
I wanted to check with you if you have any objections to removing:
 - tensorflow/contrib/verbs
 - tensorflow/contrib/gdr
 - tensorflow/contrib/mpi

in the main repository?

Or the options we have during tensorflow configure script or the build config options?

[Günhan Gülsoy]

For posterity, looks like all of these, plus mpi_collectives has moved to networking repository.

So I will proceed with the deletion.

Thanks Bairen for you help!