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/util/system.cpp

@@ -315,7 +315,7 @@ bool ArgsManager::ParseParameters(int argc, const char* const argv[], std::strin
         if (key[0] != '-') {
             if (!m_accept_any_command && m_command.empty()) {
                 // The first non-dash arg is a registered command
-                Optional<unsigned int> flags = GetArgFlags(key);
+                std::optional<unsigned int> flags = GetArgFlags(key);
                 if (!flags || !(*flags & ArgsManager::COMMAND)) {
                     error = strprintf("Invalid command '%s'", argv[i]);
                     return false;
@@ -337,7 +337,7 @@ bool ArgsManager::ParseParameters(int argc, const char* const argv[], std::strin
         key.erase(0, 1);
         std::string section;
         util::SettingsValue value = InterpretOption(section, key, val);
-        Optional<unsigned int> flags = GetArgFlags('-' + key);
+        std::optional<unsigned int> flags = GetArgFlags('-' + key);
 
         // Unknown command line options and command line options with dot
         // characters (which are returned from InterpretOption with nonempty
@@ -363,7 +363,7 @@ bool ArgsManager::ParseParameters(int argc, const char* const argv[], std::strin
     return success;
 }
 
-Optional<unsigned int> ArgsManager::GetArgFlags(const std::string& name) const
+std::optional<unsigned int> ArgsManager::GetArgFlags(const std::string& name) const
 {
     LOCK(cs_args);
     for (const auto& arg_map : m_available_args) {
@@ -372,7 +372,7 @@ Optional<unsigned int> ArgsManager::GetArgFlags(const std::string& name) const
             return search->second.m_flags;
         }
     }
-    return nullopt;
+    return std::nullopt;
 }
 
 std::optional<const ArgsManager::Command> ArgsManager::GetCommand() const
@@ -874,7 +874,7 @@ bool ArgsManager::ReadConfigStream(std::istream& stream, const std::string& file
         std::string section;
         std::string key = option.first;
         util::SettingsValue value = InterpretOption(section, key, option.second);
-        Optional<unsigned int> flags = GetArgFlags('-' + key);
+        std::optional<unsigned int> flags = GetArgFlags('-' + key);
         if (flags) {
             if (!CheckValid(key, value, *flags, error)) {
                 return false;
@@ -1034,7 +1034,7 @@ void ArgsManager::logArgsPrefix(
     std::string section_str = section.empty() ? "" : "[" + section + "] ";
     for (const auto& arg : args) {
         for (const auto& value : arg.second) {
-            Optional<unsigned int> flags = GetArgFlags('-' + arg.first);
+            std::optional<unsigned int> flags = GetArgFlags('-' + arg.first);
             if (flags) {
                 std::string value_str = (*flags & SENSITIVE) ? "****" : value.write();
                 LogPrintf("%s %s%s=%s\n", prefix, section_str, arg.first, value_str);

src/util/system.h

@@ -19,7 +19,7 @@
 #include <compat/assumptions.h>
 #include <fs.h>
 #include <logging.h>
-#include <optional.h>
+#include <optional>
 #include <sync.h>
 #include <tinyformat.h>
 #include <util/settings.h>
@@ -375,7 +375,7 @@ public:
      * Return Flags for known arg.
      * Return nullopt for unknown arg.
      */
-    Optional<unsigned int> GetArgFlags(const std::string& name) const;
+    std::optional<unsigned int> GetArgFlags(const std::string& name) const;
 
     /**
      * Read and update settings file with saved settings. This needs to be