Minor tweaks in machine limits handling:

- renamed some variables so the names are not misleading
- improved readability a bit
- disabled silent mode for RRF (it was apparently enabled by mistake)
- set default value of machine_limits_usage to TimeEstimateOnly

src/libslic3r/PrintConfig.cpp

@@ -1614,7 +1614,7 @@ void PrintConfigDef::init_fff_params()
     def->enum_labels.push_back(L("Use for time estimate"));
     def->enum_labels.push_back(L("Ignore"));
     def->mode = comAdvanced;
-    def->set_default_value(new ConfigOptionEnum<MachineLimitsUsage>(MachineLimitsUsage::EmitToGCode));
+    def->set_default_value(new ConfigOptionEnum<MachineLimitsUsage>(MachineLimitsUsage::TimeEstimateOnly));
 
     {
         struct AxisDefault {