ComboProperty: rm many unused member fcts and operators

GUI/Model/Tune/FitParameterItem.cpp

@@ -134,20 +134,12 @@ namespace {
 
 ComboProperty fitParameterTypeCombo()
 {
-    QStringList tooltips = QStringList() << "Fixed at given value"
-                                         << "Limited in the range [min, max]"
-                                         << "Limited at lower bound [min, inf]"
-                                         << "Limited at upper bound [-inf, max]"
-                                         << "No limits imposed to parameter value";
-
-    ComboProperty result;
-    result << "fixed"
-           << "limited"
-           << "lower limited"
-           << "upper limited"
-           << "free";
+    auto result =
+        ComboProperty::fromList({"fixed", "limited", "lower limited", "upper limited", "free"});
     result.setCurrentValue("limited");
-    result.setToolTips(tooltips);
+    result.setToolTips({"Fixed at given value", "Limited in the range [min, max]",
+                        "Limited at lower bound [min, inf]", "Limited at upper bound [-inf, max]",
+                        "No limits imposed to parameter value"});
     return result;
 }