fix: Remove fixed width setting for dropdown popup shell (#1612)

Author: jdneo

com.microsoft.copilot.eclipse.ui/src/com/microsoft/copilot/eclipse/ui/swt/DropdownPopup.java

@@ -215,7 +215,6 @@ void open(Point location, List<DropdownItemGroup> groups, String selectedItemId,
     });
 
     shell.pack();
-    shell.setSize(SHORT_POPUP_WIDTH, shell.getSize().y);
     constrainHeightIfNeeded();
     adjustBounds(location, anchorHeight);
     scrollToFocusedItem();