bin: make signal handler simple (#3614)
bin: make signal handler simple (#3614)

free() on signal handler causes "ThreadSanitizer: signal-unsafe call inside of a signal"
  Currently, signal handler only unblocks main loop.

Signed-off-by: Takahiro Yamashita <8b9f03f78cb27351a99f79113f99e589b65190d5@gmail.com>
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