Change install requirements for lm-eval (#2453)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2453

Previously, explicit `datasets`  and `lm-eval` package versions were required due to conflicting requirements with ET.

As a result of recent pin and requirement bumps, the conflicts are resolved.

Removing explicit versions

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Reviewed By: larryliu0820

Differential Revision: D54934068

fbshipit-source-id: 5b54812511e7e30d77842c8c824ddd09aed99780