Optimize temp files removal

[xonixx]

Now synthetic test is ~twice slower compared to tush.

$ time tush-check 1000.tush 

real    0m1.055s
user    0m0.787s
sys     0m0.180s
$ time ./fhtagn.awk 1000.tush 

real    0m1.982s
user    0m1.765s
sys     0m0.294s

This is due to calling system("rm -f " stdOutF " " stdErrF) for every test. Can we call rm one time for all temp files at the end?

[xonixx]

Ok, now it's faster.

$ time ./fhtagn.awk 1000.tush 

real    0m0.841s
user    0m0.728s
sys     0m0.146s