Delete unused temp dir in tests
Delete unused temp dir in tests

Summary:
`_Instance.__init__` sets base_dir, then immediately calls `_init_state`. `_init_state` overrides base_dir, making the earlier assignment pointless.

Remove the dead store to base_dir and the unused temporary directory.

This diff should not change behavior.

Reviewed By: simpkins

Differential Revision: D14294179

fbshipit-source-id: b159c99da581d61e5b843a2a9bca5c1f35b9e222

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