Revert D32780415: [Static Runtime] Move implementation details from impl.h into internal.h
Test Plan: revert-hammer
Differential Revision:
D32780415 (https://github.com/pytorch/pytorch/commit/999e93e6a89baa0696204cb7485e97bacc09a573)
Original commit changeset: 119b7aedbf56
fbshipit-source-id: 1aa777e8c1854ab27e86bc625188f7170097fac8
