hush: do not print killing signal name in `cmd_whihc_dies_on_signal`

function                                             old     new   delta
process_wait_result                                  438     449     +11

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush_test/hush-psubst/tick6.right b/shell/hush_test/hush-psubst/tick6.right
new file mode 100644
index 0000000..065fd3e
--- /dev/null
+++ b/shell/hush_test/hush-psubst/tick6.right
@@ -0,0 +1 @@
+137