unotools: remove not needed UcbStreamHelper inheritance

This class only has static member functions, nothing requires that
inheritance.

Change-Id: I31db802d0a9dcda01772b1e09a68af770868358d
Reviewed-on: https://gerrit.libreoffice.org/45924Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>

include/unotools/ucbstreamhelper.hxx

@@ -49,7 +49,7 @@ namespace utl
 {
     class UcbLockBytesHandler;
 
-    class UNOTOOLS_DLLPUBLIC UcbStreamHelper : public SvStream
+    class UNOTOOLS_DLLPUBLIC UcbStreamHelper
     {
     public:
         static SvStream*    CreateStream( const OUString& rFileName, StreamMode eOpenMode );