cppcheck warns with publicAllocationError in
INetMIMECharsetList_Impl::prepend(...)
>     { m_pFirst = new Node(rCharset, m_pFirst); }<--- Possible leak
> in public function. The pointer 'm_pFirst' is not deallocated before
> it is allocated.

We got a single linked list here which is correctly deallocated
in dtor.

But with C++11 std::forward_list there is no reason to implement or own
list.

Change-Id: Ia6582061c1e5f1284bd81fafef88ce475ee891aa
Reviewed-on: https://gerrit.libreoffice.org/31132Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>