Remove the extra height hack from wxToolBar::DoGetBestSize()

There doesn't seem to be any good reason to add 3px to the vertical
component of the toolbar best size and it's not clear how can the
original problem be reproduced.

This basically reverts c118d8b06e.

src/msw/toolbar.cpp

@@ -597,14 +597,6 @@ wxSize wxToolBar::DoGetBestSize() const
                 sizeBest.IncTo(wxSize(-1, MSWGetFittingtSizeForControl(tool).y));
             }
         }
-
-        // Without the extra height, DoGetBestSize can report a size that's
-        // smaller than the actual window, causing windows to overlap slightly
-        // in some circumstances, leading to missing borders (especially noticeable
-        // in AUI layouts).
-        if (!(GetWindowStyle() & wxTB_NODIVIDER))
-            sizeBest.y += 2;
-        sizeBest.y ++;
     }
 
     return sizeBest;