[PyTorch] Outline destructor of CppFunction (#63688)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63688
CppFunction is used for function registration, so it's not performance-sensitive. Outlining the destructor should reduce code size.
ghstack-source-id: 146648927
Test Plan: Mobile buildsizebot
Reviewed By: dhruvbird
Differential Revision: D30462640
fbshipit-source-id: de410f933bf936c16769a10a52092469007c8487
