Removes SymbolicVariable from tests (#24007)
Summary:
This PR removes SymbolicVariable from all tests as well as the specialize_autogradzero and canonicalize_ops passes. These passes used SymbolicVariable in a relatively simple way compared to its few remaining uses.
Removing SymbolicVariable means graphs must be constructed by other methods. IRParser was preferred for tests, but tests requiring pointers to graph internals or differentiation use direct construction instead. See https://github.com/pytorch/pytorch/issues/23989, which was discovered during this process, for why IRParser cannot be used when differentiation is required. Direct construction was also used in the updated passes.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24007
Test Plan: Only refactors existing tests and preserves current checks; no additional testing needed.
Differential Revision: D16906045
Pulled By: mruberry
fbshipit-source-id: b67df4611562cd7618f969890e2b6840750c7266
