[Benchmarking] Nit: don't convert to list first

Bug: 1030840
Change-Id: I5cc64282e9405935686cbb9b6d249fd4d3d462e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1974393
Auto-Submit: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: John Chen <johnchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726081}

tools/perf/core/bot_platforms.py

@@ -44,7 +44,7 @@ class PerfPlatform(object):
           _IsPlatformSupported(b.benchmark, self._platform_os)])
     # pylint: enable=redefined-outer-name
     benchmark_names = [config.name for config in self._benchmark_configs]
-    assert len(list(set(benchmark_names))) == len(benchmark_names), (
+    assert len(set(benchmark_names)) == len(benchmark_names), (
         'Make sure that a benchmark does not appear twice.')
 
     base_file_name = name.replace(' ', '_').lower()