Remove incomplete paragraph from QSet::iterator documentation

I could trace the dangling 'However, ' back to Qt 4.2. We probably will
never knew what the rest of the sentence was, exactly ... since the
previous paragraph is anyhow covering the same grounds we can just
remove the paragraph.

Change-Id: I1dda56e1ad17932205b8f40a527ca90a7592ad40
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qset.qdoc

@@ -621,9 +621,6 @@
     unless you need to change the QSet through the iterator. Const
     iterators are slightly faster, and can improve code readability.
 
-    QSet\<T\>::iterator allows you to iterate over a QSet\<T\> and
-    modify it as you go (using QSet::erase()). However,
-
     The default QSet::iterator constructor creates an uninitialized
     iterator. You must initialize it using a function like
     QSet::begin(), QSet::end(), or QSet::insert() before you can