perf test: Fix double word in comments

Delete the redundant word "then" in comments.

Signed-off-by: shaomin Deng <dengshaomin@cdjrlc.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20220807074753.7857-1-dengshaomin@cdjrlc.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>