Do not gate or hide experimental settings

This is somewhat hacky fix just for 2.15. I unintentionally hid them
from the manual, when no one wanted to hide them that (including
myself). I also required the experimental feature to be enabled in an
order-dependent way, which is not good.

The simplest fix for this immanent release is just to always show them,
and always allow them to be set.

Effectively undoes some changes from aa663b7e89

src/libutil/config.cc

@@ -70,17 +70,10 @@ void AbstractConfig::reapplyUnknownSettings()
         set(s.first, s.second);
 }
 
-// Whether we should process the option. Excludes aliases, which are handled elsewhere, and disabled features.
-static bool applicable(const Config::SettingData & sd)
-{
-    return !sd.isAlias
-        && experimentalFeatureSettings.isEnabled(sd.setting->experimentalFeature);
-}
-
 void Config::getSettings(std::map<std::string, SettingInfo> & res, bool overriddenOnly)
 {
     for (auto & opt : _settings)
-        if (applicable(opt.second) && (!overriddenOnly || opt.second.setting->overridden))
+        if (!opt.second.isAlias && (!overriddenOnly || opt.second.setting->overridden))
             res.emplace(opt.first, SettingInfo{opt.second.setting->to_string(), opt.second.setting->description});
 }
 
@@ -154,7 +147,7 @@ nlohmann::json Config::toJSON()
 {
     auto res = nlohmann::json::object();
     for (auto & s : _settings)
-        if (applicable(s.second))
+        if (!s.second.isAlias)
             res.emplace(s.first, s.second.setting->toJSON());
     return res;
 }
@@ -163,7 +156,7 @@ std::string Config::toKeyValue()
 {
     auto res = std::string();
     for (auto & s : _settings)
-        if (applicable(s.second))
+        if (s.second.isAlias)
             res += fmt("%s = %s\n", s.first, s.second.setting->to_string());
     return res;
 }
@@ -171,9 +164,6 @@ std::string Config::toKeyValue()
 void Config::convertToArgs(Args & args, const std::string & category)
 {
     for (auto & s : _settings) {
-        /* We do include args for settings gated on disabled
-           experimental-features. The args themselves however will also be
-           gated on any experimental feature the underlying setting is. */
         if (!s.second.isAlias)
             s.second.setting->convertToArg(args, category);
     }