Move autograd function for CrossMapLRN2d from being backend specific to modules/_functions. (#25339)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25339
This is to get rid of backend-specific dispatch in modules; this autograd function is no longer backend specific so
doesn't need to be in a backend specific location.
Test Plan: Imported from OSS
Differential Revision: D17101576
Pulled By: gchanan
fbshipit-source-id: f4f0bd3ecc2d4dbd8cdfedbaabcadb8c603d2507
