remove backward functions from jit-op-registry for mobile build (#26851)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26851
Add codegen option to remove backward ops from jit-op-registry as they are not
likely to be used for inference only mobile build.
Measured ARM-v7 AAR build size change: 5,804,182 -> 5,331,219.
Test Plan: - build and integrate with demo app;
Differential Revision: D17587422
Pulled By: ljk53
fbshipit-source-id: 08c0fc7a710698a0d4baaf16bbb73cb812b1126a
