Remove aria-haspopup from dropdowns (#33624)

`aria-haspopup="true"` is really intended to signal that an ARIA `menu` will be opened on activation. as a result, some assistive technologies will announce controls with `aria-haspopup="true"` as a menu or menu item (e.g. JAWS and NVDA).
In addition, `aria-haspopup` seems to trigger a bug in Edge/Narrator where the `aria-expanded` state is not correctly announced at the moment when `aria-haspopup` is present.
This now makes the dropdown button more like a generic disclosure widget control - see also https://www.w3.org/TR/wai-aria-practices-1.2/examples/disclosure/disclosure-navigation.html01

site/content/docs/4.6/components/scrollspy.md

@@ -33,7 +33,7 @@ Scroll the area below the navbar and watch the active class change. The dropdown
         <a class="nav-link" href="#mdo">@mdo</a>
       </li>
       <li class="nav-item dropdown">
-        <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">Dropdown</a>
+        <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-expanded="false">Dropdown</a>
         <div class="dropdown-menu">
           <a class="dropdown-item" href="#one">one</a>
           <a class="dropdown-item" href="#two">two</a>
@@ -69,7 +69,7 @@ Scroll the area below the navbar and watch the active class change. The dropdown
       <a class="nav-link" href="#mdo">@mdo</a>
     </li>
     <li class="nav-item dropdown">
-      <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">Dropdown</a>
+      <a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-expanded="false">Dropdown</a>
       <div class="dropdown-menu">
         <a class="dropdown-item" href="#one">one</a>
         <a class="dropdown-item" href="#two">two</a>