Make SignatureExtractorChecker private to its own file

It's only used here in DataFromTransaction

Author: Empact

src/script/sign.cpp

@@ -243,6 +243,7 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
     return sigdata.complete;
 }
 
+namespace {
 class SignatureExtractorChecker final : public BaseSignatureChecker
 {
 private:
@@ -251,21 +252,17 @@ class SignatureExtractorChecker final : public BaseSignatureChecker
 
 public:
     SignatureExtractorChecker(SignatureData& sigdata, BaseSignatureChecker& checker) : sigdata(sigdata), checker(checker) {}
-    bool CheckSig(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override;
-};
-
-bool SignatureExtractorChecker::CheckSig(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const
-{
-    if (checker.CheckSig(scriptSig, vchPubKey, scriptCode, sigversion)) {
-        CPubKey pubkey(vchPubKey);
-        sigdata.signatures.emplace(pubkey.GetID(), SigPair(pubkey, scriptSig));
-        return true;
+    bool CheckSig(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override
+    {
+        if (checker.CheckSig(scriptSig, vchPubKey, scriptCode, sigversion)) {
+            CPubKey pubkey(vchPubKey);
+            sigdata.signatures.emplace(pubkey.GetID(), SigPair(pubkey, scriptSig));
+            return true;
+        }
+        return false;
     }
-    return false;
-}
+};
 
-namespace
-{
 struct Stacks
 {
     std::vector<valtype> script;