scripted-diff: remove Optional & nullopt

-BEGIN VERIFY SCRIPT-
git rm src/optional.h

sed -i -e 's/Optional</std::optional</g' $(git grep -l 'Optional<' src)

sed -i -e 's/{nullopt}/{std::nullopt}/g' $(git grep -l 'nullopt' src)
sed -i -e 's/ nullopt;/ std::nullopt;/g' $(git grep -l 'nullopt' src)
sed -i -e 's/ nullopt)/ std::nullopt)/g' $(git grep -l 'nullopt' src)
sed -i -e 's/(nullopt)/(std::nullopt)/g' $(git grep -l 'nullopt' src)
sed -i -e 's/ nullopt,/ std::nullopt,/g' $(git grep -l 'nullopt' src)
sed -i -e 's/? nullopt :/? std::nullopt :/g' $(git grep -l 'nullopt' src)
sed -i -e 's/: nullopt}/: std::nullopt}/g' $(git grep -l 'nullopt' src)

sed -i -e '/optional.h \\/d' src/Makefile.am

sed -i -e '/#include <optional.h>/d' src/test/fuzz/autofile.cpp src/test/fuzz/buffered_file.cpp src/test/fuzz/node_eviction.cpp

sed -i -e 's/#include <optional.h>/#include <optional>/g' $(git grep -l '#include <optional.h>' src)
-END VERIFY SCRIPT-

src/validation.h

@@ -17,7 +17,7 @@
 #include <crypto/common.h> // for ReadLE64
 #include <fs.h>
 #include <node/utxo_snapshot.h>
-#include <optional.h>
+#include <optional>
 #include <policy/feerate.h>
 #include <protocol.h> // For CMessageHeader::MessageStartChars
 #include <script/script_error.h>
@@ -206,7 +206,7 @@ struct MempoolAcceptResult {
     /** Constructor for failure case */
     explicit MempoolAcceptResult(TxValidationState state)
         : m_result_type(ResultType::INVALID),
-        m_state(state), m_replaced_transactions(nullopt), m_base_fees(nullopt) {
+        m_state(state), m_replaced_transactions(std::nullopt), m_base_fees(std::nullopt) {
             Assume(!state.IsValid()); // Can be invalid or error
         }
 
@@ -924,7 +924,7 @@ public:
 
     bool IsSnapshotActive() const;
 
-    Optional<uint256> SnapshotBlockhash() const;
+    std::optional<uint256> SnapshotBlockhash() const;
 
     //! Is there a snapshot in use and has it been fully validated?
     bool IsSnapshotValidated() const { return m_snapshot_validated; }