Chutney doesn't remove temporary files after processing warnings

When the Chutney test-network script ends, it displays warnings from the tor logs. It summarizes/filters them in the show_warnings() function in tools/warnings.sh. This function creates two files with LOGS=$(mktemp) and FILTERED_LOGS=$(mktemp) but never deletes them when it's done.

The proposal is to add rm "${LOGS}" "${FILTERED_LOGS}" at the end of the function.