Remove uncessary header

gt-workbench/exercise2/example.cc

-// graph-tool -- a general graph modification and manipulation thingy
-//
-// Copyright (C) 2006-2025 Tiago de Paula Peixoto <tiago@skewed.de>
-//
-// This program is free software; you can redistribute it and/or modify it under
-// the terms of the GNU Lesser General Public License as published by the Free
-// Software Foundation; either version 3 of the License, or (at your option) any
-// later version.
-//
-// This program is distributed in the hope that it will be useful, but WITHOUT
-// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
-// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
-// details.
-//
-// You should have received a copy of the GNU Lesser General Public License
-// along with this program. If not, see <http://www.gnu.org/licenses/>.
-
 #include <boost/python.hpp>
 
 #include "example.hh"