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.cpp

@@ -23,7 +23,7 @@
 #include <logging/timer.h>
 #include <node/coinstats.h>
 #include <node/ui_interface.h>
-#include <optional.h>
+#include <optional>
 #include <policy/policy.h>
 #include <policy/settings.h>
 #include <pow.h>
@@ -5175,7 +5175,7 @@ double GuessVerificationProgress(const ChainTxData& data, const CBlockIndex *pin
     return std::min<double>(pindex->nChainTx / fTxTotal, 1.0);
 }
 
-Optional<uint256> ChainstateManager::SnapshotBlockhash() const {
+std::optional<uint256> ChainstateManager::SnapshotBlockhash() const {
     LOCK(::cs_main);
     if (m_active_chainstate != nullptr &&
             !m_active_chainstate->m_from_snapshot_blockhash.IsNull()) {