gem5.sh: simplify, and do m5 resetstats and m5 exit

This covers the most common use case of running a benchmark after restore.

gem5-bench-cache

@@ -83,14 +83,9 @@ fi
 
 # Restore and run benchmarks.
 rm -f "$results_file"
-printf '#!/bin/sh
-m5 resetstats
-dhrystone XXX
-m5 exit
-' >"${common_gem5_readfile_file}"
 for n in 1000 10000 100000; do
   printf "n ${n}\n" >> "$results_file"
-  sed -Ei "s/^dhrystone .*/dhrystone ${n}/" "${common_gem5_readfile_file}"
+  printf "dhrystone ${n}" > "${common_gem5_readfile_file}"
   bench-all
   printf "\n" >> "$results_file"
 done