don't assert contracts during local runs (for consistency with CI runs)

Author: Carolyn Zech

scripts/run-kani.sh

@@ -292,6 +292,7 @@ main() {
             echo "Running Kani verify-std command..."
             "$kani_path" verify-std -Z unstable-options ./library \
                 $unstable_args \
+                --no-assert-contracts \
                 $command_args \
                 --enable-unstable \
                 --cbmc-args --object-bits 12