damo_schemes: Ignore error of turning DAMON off in cleanup_exit()

As the comment says, we can ignore turn_damon_off() error in
damo-schemes cleanup, similar to that of damo_record.  However, it is
not really ignoring it but prints message.  It makes people confused[1].
Ignore the error in real.

[1] #53

Signed-off-by: SeongJae Park <sj38.park@gmail.com>

damo_schemes.py

@@ -12,9 +12,7 @@
 
 def cleanup_exit(exit_code):
     # ignore returning error, as kdamonds may already finished
-    err = _damon.turn_damon_off(kdamonds_idxs)
-    if err:
-        print('failed to turn damon off (%s)' % err)
+    _damon.turn_damon_off(kdamonds_idxs)
     err = _damon.stage_kdamonds(orig_kdamonds)
     if err:
         print('failed restoring previous kdamonds setup (%s)' % err)