Remove Qt 4.8 index.html from qt.index.

That works around an issue with name collision pages in qdoc from Qt5.

Task-number: QTCREATORBUG-8415
Change-Id: I289a80174b006424d54f98410b2635a27258e368
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>

doc/qt.index

@@ -4523,9 +4523,6 @@
             <contents name="implicit-sharing-in-detail" title="Implicit Sharing in Detail" level="1"/>
             <contents name="list-of-classes" title="List of Classes" level="1"/>
         </page>
-        <page access="public" status="commendable" name="index.html" href="index.html" subtype="page" title="" fulltitle="" subtitle="" location="index.qdoc">
-            <keyword name="qt-reference-documentation"/>
-        </page>
         <page access="public" status="commendable" name="install-Symbian-installer.html" href="install-symbian-installer.html" subtype="page" title="Installing Qt for the Symbian platform from a Binary Package" fulltitle="Installing Qt for the Symbian platform from a Binary Package" subtitle="" location="installation.qdoc"/>
         <page access="public" status="commendable" name="install-Symbian.html" href="install-symbian.html" subtype="page" title="Installing Qt for the Symbian Platform" fulltitle="Installing Qt for the Symbian Platform" subtitle="" location="installation.qdoc">
             <contents name="step-1-set-up-the-development-environment" title="Step 1: Set Up the Development Environment" level="1"/>