nanobench: Stop reporting median_ms, it's no better than min_ms.

bench/nanobench.cpp

Index: bench/nanobench.cpp
diff --git a/bench/nanobench.cpp b/bench/nanobench.cpp
index df6bcd753102493c6b0bc6f65af65808b66a1700..3a3bca673f3f0c61a0131dfe4374e77980ff2dfc 100644
--- a/bench/nanobench.cpp
+++ b/bench/nanobench.cpp
@@ -1200,7 +1200,6 @@ int nanobench_main() {
             benchStream.fillCurrentOptions(log.get());
             target->fillOptions(log.get());
             log->metric("min_ms",    stats.min);
-            log->metric("median_ms", stats.median);
 #if SK_SUPPORT_GPU
             if (gpuStatsDump) {
                 // dump to json, only SKPBench currently returns valid keys / values