Remove ConfigCompatibilityValidator, fix #2599

Author: AndreyAkinshin

src/BenchmarkDotNet/Reports/Summary.cs

@@ -160,7 +160,7 @@ private static IOrderer GetConfiguredOrdererOrDefaultOne(IEnumerable<ImmutableCo
                    .Where(config => config.Orderer != DefaultOrderer.Instance)
                    .Select(config => config.Orderer)
                    .Distinct()
-                   .SingleOrDefault()
+                   .FirstOrDefault()
                ?? DefaultOrderer.Instance;
 
         private static SummaryStyle GetConfiguredSummaryStyleOrDefaultOne(ImmutableArray<BenchmarkCase> benchmarkCases)
@@ -173,7 +173,7 @@ private static SummaryStyle GetConfiguredSummaryStyleOrDefaultOne(ImmutableArray
 #nullable enable
                    .Select(benchmark => benchmark.Config.SummaryStyle)
                    .Distinct()
-                   .SingleOrDefault()
+                   .FirstOrDefault()
                ?? SummaryStyle.Default;
 
         // TODO: GcStats

src/BenchmarkDotNet/Running/BenchmarkRunnerClean.cs

@@ -353,17 +353,6 @@ private static ImmutableArray<ValidationError> Validate(params BenchmarkRunInfo[
         {
             var validationErrors = new List<ValidationError>();
 
-            if (benchmarks.Any(b => b.Config.Options.IsSet(ConfigOptions.JoinSummary)))
-            {
-                var joinedCases = benchmarks.SelectMany(b => b.BenchmarksCases).ToArray();
-
-                validationErrors.AddRange(
-                    ConfigCompatibilityValidator
-                        .FailOnError
-                        .Validate(new ValidationParameters(joinedCases, null))
-                    );
-            }
-
             foreach (var benchmarkRunInfo in benchmarks)
                 validationErrors.AddRange(benchmarkRunInfo.Config.GetCompositeValidator().Validate(new ValidationParameters(benchmarkRunInfo.BenchmarksCases, benchmarkRunInfo.Config)));