Remove Legacy Code

[f-allian]

After consulting with @jmafoster1 we've agreed that the following directories/scripts in the codebase are redundant and will be removed:

• data_collector.py in the /data_collection directory, which includes the DataCollector class and its daughter classes ExperimentalDataCollector and ObservationalDataCollector.
• enum_gen.py and abstract_causal_test_case.py in the /generation directory contain the AbstractCausalTestCase class and the EnumGen.
• All aspects of the z3 package will be removed and deprecated in future versions.

[f-allian]

@jmafoster1 Does the BaseTestCase class need removing too? See: https://github.com/CITCOM-project/CausalTestingFramework/blob/main/causal_testing/testing/base_test_case.py

[jmafoster1]

No, I think that needs to stay. It's a data class for a couple of other things. I don't love it, but we agreed a while ago that it's the least worst way of doing things.

[f-allian]

Closed by #309.