fixed u6.3 compile error > replaced unity.guid generation with pure c#

Author: robertdorn83

Editor/Scripts/Interactivity/VisualScriptingExport/UnitExporters/Flow/SelectOnFlowUnitExporter.cs

@@ -34,12 +34,7 @@ public bool InitializeInteractivityNodes(UnitExporter unitExporter)
             int typeIndex = 0;
 
             // using VariableKind.Scene, because we already generated a unique name for the variable
-#if UNITY_6000_3_OR_NEWER
-            var newGUID = UnityEngine.GUID.Generate().ToString();
-#else
-            var newGUID = GUID.Generate().ToString();
-#endif
-            var varIndex = unitExporter.vsExportContext.AddVariableWithIdIfNeeded($"SelectOnFlowValue_{newGUID}", null, VariableKind.Scene, typeIndex);
+            var varIndex = unitExporter.vsExportContext.AddVariableWithIdIfNeeded($"SelectOnFlowValue_{System.Guid.NewGuid().ToString()}", null, VariableKind.Scene, typeIndex);
 
             var getVar = VariablesHelpers.GetVariable(unitExporter, varIndex, out var getVarValue);
             getVarValue.MapToPort(unit.selection);