All4x4Tables: BUG lost implications after pruning

The script at `equational_theories/Generated/All4x4Tables/src/generate_lean.py`
is supposed to read the implications.json file, and prune the finite magma
checks based on that, so that we don't have to generate redundant explicit
refutations that already follow from the known implications.

I recently ported this script to work with the cancellative magmas added
in teorth#224.

Unfortunately, there seems to be a bug in this naive port: once we move to
implicit refutations, the total proof_false decreases, and the number of
unknowns increases. For example, running on a now-recent main we have

```
BEFORE (explicit proofs in All4x4Tables):
{"explicit_proof_true": 28263,
"implicit_proof_true": 5457962,
"unknown": 2726304,
"implicit_proof_false": 3486,
"explicit_proof_false": 13845794
}

AFTER (implicit proofs in All4x4Tables):
{"explicit_proof_true": 28263,
"implicit_proof_true": 5457962,
"unknown": 2744422,
"implicit_proof_false": 13185894,
"explicit_proof_false": 645268
}
```

To reproduce,

1. Generate an `implications.json` using
 `lake exe extract_implications  --json --only-implications equational_theories`

2. Run the version of `generate_lean.py` from this commit.

3. Build the proofs, then inspect the output of
 `lake exe extract_implications outcomes --hist`.