Refactor integration tests

Previously some integration tests for greeter and frc46_factory_token were compiled in the crates themselves. However, this brings in the `fvm` as a dependency for the crate which prevents them from being built by the new helix_test_actors package properly.

In https://github.com/helix-onchain/filecoin/pull/217 those tests were simply deleted to unblock consumers waiting for crate updates but the tests should be added back in alongside the other integration tests.