menu: remove winbar code

No unmerged Vim patch, applicable to Neovim, depend on WinBar feature.
It was merged only for merging Vim patches.
It is currently useless in Neovim.
Remove it to avoid rendering issues.

Close https://github.com/neovim/neovim/issues/12689

src/nvim/buffer_defs.h

@@ -1132,12 +1132,6 @@ struct VimMenu {
   vimmenu_T   *next;                 ///< Next item in menu
 };
 
-typedef struct {
-  int wb_startcol;
-  int wb_endcol;
-  vimmenu_T *wb_menu;
-} winbar_item_T;
-
 /// Structure which contains all information that belongs to a window.
 ///
 /// All row numbers are relative to the start of the window, except w_winrow.
@@ -1354,10 +1348,6 @@ struct window_S {
 
   char_u      *w_localdir;          /* absolute path of local directory or
                                        NULL */
-  vimmenu_T *w_winbar;            // The root of the WinBar menu hierarchy.
-  winbar_item_T *w_winbar_items;  // list of items in the WinBar
-  int w_winbar_height;            // 1 if there is a window toolbar
-
   // Options local to a window.
   // They are local because they influence the layout of the window or
   // depend on the window layout.