benchmark: remove unused field in class BenchmarkProgress

PR-URL: https://github.com/nodejs/node/pull/26925
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>

benchmark/_benchmark_progress.js

@@ -35,7 +35,6 @@ class BenchmarkProgress {
     // Number of times each file will be run (roughly).
     this.runsPerFile = queue.length / benchmarks.length;
     this.currentFile = '';  // Filename of current benchmark.
-    this.currentFileConfig;  // Configurations for current file
     // Number of configurations already run for the current file.
     this.completedConfig = 0;
     // Total number of configurations for the current file