Kill THNN version of MultiMarginCriterion; it's not used anymore.
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/30725
Test Plan: Imported from OSS
Differential Revision: D18808767
Pulled By: gchanan
fbshipit-source-id: bcc4a6e272036f3d167fc158a53fe7aa1dec51f9
