[quant][pt2e] Rename _pt2e to pt2e (#104668)
Summary:
X-link: https://github.com/pytorch/executorch/pull/3
att
Test Plan: Imported from OSS
Differential Revision: D47202807
Pull Request resolved: https://github.com/pytorch/pytorch/pull/104668
Approved by: https://github.com/andrewor14
