[pruning] Move pruning files to their own directory (#60293)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60293
Move pruning files to their own directory
Test Plan:
`buck test mode/dev-nosan //caffe2/test:ao -- TestBasePruner`
https://pxl.cl/1KCfz
Reviewed By: z-a-f
Differential Revision: D29238159
fbshipit-source-id: 0173a278b39ff5ee4cbd54f333f558b6fe412be5
