Fix navigation with offline style

When the switching to the non-simple offline style is done after
document load, the navigation to anchors completely breaks. So, do
the switch without the additional delay.

Task-number: QTCREATORBUG-18448
Change-Id: I5abbc3bbe1c743d2a5e493bb9e0916c5d092942a
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>
(cherry picked from commit 2a9f678)
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>

doc/global/qt-html-templates-offline-simple.qdocconf

@@ -6,7 +6,7 @@ qhp.extraFiles    += style/offline-simple.css
 HTML.headerstyles  = \
     "  <link rel=\"stylesheet\" type=\"text/css\" href=\"style/offline-simple.css\" />\n" \
     "  <script type=\"text/javascript\">\n" \
-    "    window.onload = function(){document.getElementsByTagName(\"link\").item(0).setAttribute(\"href\", \"style/offline.css\");};\n" \
+    "    document.getElementsByTagName(\"link\").item(0).setAttribute(\"href\", \"style/offline.css\");\n" \
     "  </script>\n"
 
 HTML.postheader = \