use delete[] to dealloc an array

Summary:
fix a bug in `db_stress` where an int array was incorrectly deallocated using delete instead of delete[]
Closes https://github.com/facebook/rocksdb/pull/3725

Differential Revision: D7634749

Pulled By: miasantreble

fbshipit-source-id: 489b776f5f4c03de1824edac5495787ec19cc910

tools/db_stress.cc

@@ -818,7 +818,7 @@ class SharedState {
       }
       assert(cf_ids.size() == static_cast<size_t>(num_no_overwrite_keys));
     }
-    delete permutation;
+    delete[] permutation;
 
     if (FLAGS_test_batches_snapshots) {
       fprintf(stdout, "No lock creation because test_batches_snapshots set\n");