Remove a checklist item that was already tested

The item referred to the cdm_ht_set_status() case where the item was
not already in the hashtable.  But that already happens naturally
when we scan the directory on startup... and we already have a test
for that.

src/test/test_consdiffmgr.c

@@ -876,7 +876,6 @@ struct testcase_t consdiffmgr_tests[] = {
   TEST(cleanup_old_diffs),
   TEST(validate),
 
-  // XXXX Test: register status when no pending entry existed?? (bug)
   // XXXX Test: non-cacheing cases of replyfn().
 
   END_OF_TESTCASES