[Test] Simplify command in StarCCM test

Signed-off-by: Hanwen <hanwenli@amazon.com>

Author: hanwen-cluster

tests/integration-tests/tests/performance_tests/test_starccm/test_starccm/starccm.results.sh

@@ -4,5 +4,5 @@ JOBID="$1"
 OUTPUT=$(scontrol show jobs ${JOBID} | grep StdOut | cut -d '=' -f 2)
 start_time=$(tail -n 250 ${OUTPUT} | grep " 501 " | awk '{print $NF}')
 end_time=$(tail -n 250 ${OUTPUT} | grep " 600 " | awk '{print $NF}')
-elapsed_time=$(python -c "print(${end_time} - ${start_time})")
+elapsed_time=$(echo "$end_time - $start_time" | bc -l)
 echo $elapsed_time