remove trivial goals from sessions

examples/braun_trees/why3session.xml

examples/braun_trees/why3shapes.gz

examples/bts/13375/why3session.xml

examples/bts/13375/why3shapes.gz

examples/bts/13853/why3session.xml

examples/bts/13853/why3shapes.gz

examples/counting_sort/why3session.xml

examples/counting_sort/why3shapes.gz

examples/defunctionalization/why3session.xml

examples/defunctionalization/why3shapes.gz

examples/dfs/why3session.xml

examples/dfs/why3shapes.gz

examples/double_wp/compiler/why3session.xml

examples/double_wp/compiler/why3shapes.gz

examples/double_wp/vm/why3session.xml

examples/double_wp/vm/why3shapes.gz

examples/fibonacci/why3session.xml

examples/fibonacci/why3shapes.gz

examples/find/why3session.xml

examples/find/why3shapes.gz