remove needless ## in REGISTER_ALLOCATOR definition. (#19261)
Summary:
remove needless ## in REGISTER_ALLOCATOR definition.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19261
Differential Revision: D15002025
Pulled By: soumith
fbshipit-source-id: 40614b1d79d1fe05ccf43f0ae5aab950e4c875c2
