Refactor integration tests

[alexytsu]

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 #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.