[Code Health] Remove stale feature flag kTpmLatencyMetrics

This feature flag has been enabled by default for a quite a while and
it seems ready for removal.

Bug: 356623856
Change-Id: I8e856dc263f6a74d1bc127bc46fbc5181b67c795
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6233615
Reviewed-by: Adam Langley <agl@chromium.org>
Commit-Queue: Awad Osman <awado@google.com>
Cr-Commit-Position: refs/heads/main@{#1417002}

crypto/unexportable_key_metrics.cc

@@ -304,15 +304,11 @@ std::string AlgorithmToString(SignatureVerifier::SignatureAlgorithm algorithm) {
 }
 
 void MaybeMeasureTpmOperations(UnexportableKeyProvider::Config config) {
-  static BASE_FEATURE(kTpmLatencyMetrics, "TpmLatencyMetrics",
-                      base::FEATURE_ENABLED_BY_DEFAULT);
-  if (base::FeatureList::IsEnabled(kTpmLatencyMetrics)) {
     base::ThreadPool::PostTask(
         FROM_HERE,
         {base::MayBlock(), base::TaskPriority::BEST_EFFORT,
          base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
         base::BindOnce(&MeasureTpmOperationsInternal, std::move(config)));
-  }
 }
 
 }  // namespace crypto