Remove ActiveIssue for #50968 (#54831)

Author: lewing

src/libraries/System.Threading.Tasks/tests/System.Runtime.CompilerServices/AsyncTaskMethodBuilderTests.cs

@@ -407,7 +407,6 @@ private static void TaskMethodBuilderT_UsesCompletedCache<T>(T result, bool shou
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50968", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser), nameof(PlatformDetection.IsMonoAOT))]
         public static void Tcs_ValidateFaultedTask()
         {
             var tcs = new TaskCompletionSource<int>();
@@ -417,7 +416,6 @@ public static void Tcs_ValidateFaultedTask()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50968", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser), nameof(PlatformDetection.IsMonoAOT))]
         public static void TaskMethodBuilder_ValidateFaultedTask()
         {
             var atmb = AsyncTaskMethodBuilder.Create();
@@ -427,7 +425,6 @@ public static void TaskMethodBuilder_ValidateFaultedTask()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50968", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser), nameof(PlatformDetection.IsMonoAOT))]
         public static void TaskMethodBuilderT_ValidateFaultedTask()
         {
             var atmbtr = AsyncTaskMethodBuilder<object>.Create();
@@ -437,7 +434,6 @@ public static void TaskMethodBuilderT_ValidateFaultedTask()
         }
 
         [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/50968", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser), nameof(PlatformDetection.IsMonoAOT))]
         public static void TrackedSyncContext_ValidateException()
         {
             SynchronizationContext previousContext = SynchronizationContext.Current;