tools: fix mksnapshot blob wrong freeing operator

PR-URL: #29384
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

tools/snapshot/snapshot_builder.cc

@@ -99,7 +99,7 @@ std::string SnapshotBuilder::Generate(
     // creator is still alive.
     main_instance->Dispose();
     result = FormatBlob(&blob, isolate_data_indexes);
-    delete blob.data;
+    delete[] blob.data;
   }
 
   per_process::v8_platform.Platform()->UnregisterIsolate(isolate);