refactor: get rid of unnecessary setup_python_defs calls

[lucidLuckylee]

We sometimes call setup_python_defs in files other than the two headers_chain_proof and chain_proof main.cairo or before a test. Can confirm that by looking at the btc_api warnings when running make unit_test. The API should only be created once in each test.

Remove setup_python_defs calls from every other file and confirm that the tests and chain_proofs are still working afterwards. If every unnecessary call is removed tests should only print the Blockstream Warning at most once.