Revert "svtools: HTML import: don't put lone surrogates in OUString"

This reverts commit fc670f63, which is no longer
needed after 08e78607 "Make reading UTF-8
strict".  The bug doc fdo67610-1.doc (aka
<https://bugs.documentfoundation.org/attachment.cgi?id=83417>) now opens fine
without hitting the assert in OUString::toUtf8.

svtools/source/svrtf/svparser.cxx

@@ -423,8 +423,7 @@ sal_uInt32 SvParser<T>::GetNextChar()
         while( 0 == nChars  && !bErr );
     }
 
-    // Note: ImplConvertUtf8ToUnicode() may produce a surrogate!
-    if (!rtl::isUnicodeCodePoint(c) || rtl::isHighSurrogate(c) || rtl::isLowSurrogate(c))
+    if ( ! rtl::isUnicodeCodePoint( c ) )
         c = '?' ;
 
     if( bErr )