remove trivial goals from sessions

examples/schorr_waite/why3session.xml

examples/schorr_waite/why3shapes.gz

examples/stdlib/bintree/why3session.xml

examples/stdlib/bintree/why3shapes.gz

examples/stdlib/list/why3session.xml

examples/stdlib/list/why3shapes.gz

examples/sumrange/why3session.xml

examples/sumrange/why3shapes.gz

examples/tortoise_and_hare/why3session.xml

examples/tortoise_and_hare/why3shapes.gz

examples/tree_height/why3session.xml

examples/tree_height/why3shapes.gz

examples/vacid_0_red_black_trees/why3session.xml

examples/vacid_0_red_black_trees/why3shapes.gz

examples/vacid_0_sparse_array/why3session.xml

examples/vacid_0_sparse_array/why3shapes.gz

...ythis_2016_matrix_multiplication/strassen/why3session.xml

...ifythis_2016_matrix_multiplication/strassen/why3shapes.gz

examples/verifythis_2017_tree_buffer/why3session.xml

examples/verifythis_2017_tree_buffer/why3shapes.gz