tests: ensure that strace does not leave sleeping processes stopped

* tests/detach-sleeping: Do not send SIGCONT to the sleeping process.
diff --git a/tests/detach-sleeping b/tests/detach-sleeping
index 33a2675..28ad663 100755
--- a/tests/detach-sleeping
+++ b/tests/detach-sleeping
@@ -24,7 +24,6 @@
 {
 	set +e
 	kill $tracee_pid
-	kill -CONT $tracee_pid
 	wait $tracee_pid 2> /dev/null
 }