MultiSelect: removed DragDropActive/preserve_existing_selection logic which seems unused + comments.

Can't find trace of early prototype for range-select but I couldn't find way to trigger this anymore. May be wrong. Will find out.

imgui_internal.h

@@ -2124,9 +2124,6 @@ struct ImGuiContext
     ImVec2                  NavWindowingAccumDeltaPos;
     ImVec2                  NavWindowingAccumDeltaSize;
 
-    // Range-Select/Multi-Select
-    ImGuiMultiSelectState   MultiSelectState;                   // FIXME-MULTISELECT: We currently don't support recursing/stacking multi-select
-
     // Render
     float                   DimBgRatio;                         // 0.0..1.0 animation when fading in a dimming background (for modal window and CTRL+TAB list)
 
@@ -2169,6 +2166,9 @@ struct ImGuiContext
     ImVector<ImGuiPtrOrIndex>       CurrentTabBarStack;
     ImVector<ImGuiShrinkWidthItem>  ShrinkWidthBuffer;
 
+    // Multi-Select state
+    ImGuiMultiSelectState           MultiSelectState;           // FIXME-MULTISELECT: We currently don't support recursing/stacking multi-select
+
     // Hover Delay system
     ImGuiID                 HoverItemDelayId;
     ImGuiID                 HoverItemDelayIdPreviousFrame;
@@ -3344,7 +3344,7 @@ namespace ImGui
     IMGUI_API int           TypingSelectFindNextSingleCharMatch(ImGuiTypingSelectRequest* req, int items_count, const char* (*get_item_name_func)(void*, int), void* user_data, int nav_item_idx);
     IMGUI_API int           TypingSelectFindBestLeadingMatch(ImGuiTypingSelectRequest* req, int items_count, const char* (*get_item_name_func)(void*, int), void* user_data);
 
-    // Multi-Select/Range-Select API
+    // Multi-Select API
     IMGUI_API void          MultiSelectItemHeader(ImGuiID id, bool* p_selected);
     IMGUI_API void          MultiSelectItemFooter(ImGuiID id, bool* p_selected, bool* p_pressed);