Fix metric panic (flashbots#209)

## 📝 Summary

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## 💡 Motivation and Context

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solve? Remove this section if not applicable. -->

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## ✅ I have completed the following steps:

* [ ] Run `make lint`
* [ ] Run `make test`
* [ ] Added tests (if applicable)

crates/rbuilder/src/telemetry/metrics.rs

@@ -89,7 +89,7 @@ register_metrics! {
     pub static BLOCK_VALIDATION_TIME: HistogramVec = HistogramVec::new(
         HistogramOpts::new("block_validation_time", "Block Validation Times (ms)")
             .buckets(exponential_buckets_range(1.0, 3000.0, 100)),
-        &["builder_name"]
+        &[]
     )
     .unwrap();
     pub static CURRENT_BLOCK: IntGauge =