Remove unused variables in fbpcs/emp_games/pcf2_shard_combiner/util/A…

…ggMetricsThresholdCheckers_impl.h

Summary:
LLVM-15 has a warning `-Wunused-but-set-variable` which we treat as an error because it's so often diagnostic of a code issue. Unused variables can compromise readability or, worse, performance.

This diff either (a) removes an unused variable and, possibly, it's associated code, or (b) qualifies the variable with `[[maybe_unused]]`, mostly in cases where the variable _is_ used, but, eg, in an `assert` statement that isn't present in production code.

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Reviewed By: danzimm, meyering

Differential Revision: D52849677

fbpcs/emp_games/pcf2_shard_combiner/util/AggMetricsThresholdCheckers_impl.h

@@ -157,11 +157,11 @@ checkThresholdAndUpdateMetric(
     return getGroupLiftChecker<schedulerId, usingBatch, inputEncryption>(
         threshold, sentinelVal);
   } else {
-    return [threshold, sentinelVal](
-               AggMetrics_sp<schedulerId, usingBatch, inputEncryption>) {
-      // for any other type do nothing.
-      XLOG(WARN) << "Threshold: " << threshold << " is unused";
-    };
+    return
+        [threshold](AggMetrics_sp<schedulerId, usingBatch, inputEncryption>) {
+          // for any other type do nothing.
+          XLOG(WARN) << "Threshold: " << threshold << " is unused";
+        };
   }
 }