Tests/Python: move [self_address_*.tz] to [tests_python/contracts_*]

Context

In #4008 (closed) we will move all michelson scripts used for integration scripts to a central location. To make this move more smooth, it's easier if scripts are stored in a coherent manner. The self_address_* scripts existed both in the tezt/tests/contracts and in the tests_python/contracts_015 folder. It is used primarily by tezt/tests/self_address_transfer.ml, but indirectly by the contract_typechecking.ml and TestScriptHashRegression.

In this MR, I remove the script from the tezt/tests/contracts folder and add it to all folders tests_python/contracts_*. The script applies to all active protocol versions, so this makes sense. This also ensures that the script appears in typechecking and hash regression tests for all protos. The python_tests script organization is worse than the one used by Michelson_script, but this lays the way for a smoother migration of all scripts from the latter to the former in #4008 (closed).

Manually testing the MR

Checklist

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