Revert D24269034: [fx] Refactor Tracer so that find_module and root args creation could be overridden by implementations
Test Plan: revert-hammer
Differential Revision:
D24269034 (https://github.com/pytorch/pytorch/commit/7b2e8bec851f078b53e83f5fdf0e0386c2cafdd8)
Original commit changeset: d7b67f2349dd
fbshipit-source-id: 7dd709b585f82d52d9b9973508137e36d5b5871e
