[E-ACSL] dataflow optimisation: ignore duplicated function contract

src/plugins/e-acsl/TODO

src/plugins/e-acsl/pre_analysis.ml

...s/e-acsl/tests/e-acsl-runtime/oracle/bts1324.1.res.oracle

...ins/e-acsl/tests/e-acsl-runtime/oracle/bts1324.res.oracle

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_bts1324.c

...plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_bts13242.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_bts1390.c

...plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_bts13902.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_valid.c

src/plugins/e-acsl/tests/e-acsl-runtime/oracle/gen_valid2.c

...-acsl/tests/e-acsl-runtime/oracle/gen_valid_in_contract.c

...acsl/tests/e-acsl-runtime/oracle/gen_valid_in_contract2.c

...ests/e-acsl-runtime/oracle/valid_in_contract.1.res.oracle

.../tests/e-acsl-runtime/oracle/valid_in_contract.res.oracle