go-bip39 gone from go.mod and go.sum (#72)

What is on `next`, reviewed.

- go-bip39 is gone from `go.mod` and `go.sum`: keyfunc now requires `sneak/secret` at `ef0ae90`, the commit that gives `secret` its own copy (sneak/secret#130). No derived key, mnemonic or test vector changes.

To know before merging:

- `secret`'s module is now `sneak.berlin/go/secret` (sneak/secret#43), so keyfunc's requirement, its two imports of `secret`'s `bip85` package and one README sentence use that path. The Go module proxy serves that path, so `go install` keeps working.

Model: opus-5-5
Reviewed-on: #72
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>

internal/childmnemonic/childmnemonic.go

@@ -5,10 +5,10 @@ import (
 	"errors"
 	"fmt"
 
-	"git.eeqj.de/sneak/secret/pkg/bip85"
 	"github.com/btcsuite/btcd/btcutil/hdkeychain"
 	"sneak.berlin/go/keyfunc/internal/bip39"
 	"sneak.berlin/go/keyfunc/internal/derive"
+	"sneak.berlin/go/secret/pkg/bip85"
 )
 
 // english is the number BIP-85 gives the English word list.