Post-merge cleanup

Author: edwardneal

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlConnection.cs

@@ -1416,6 +1416,7 @@ public void Open(SqlConnectionOverrides overrides)
                 try
                 {
                     statistics = SqlStatistics.StartTimer(Statistics);
+
                     if (!(IsProviderRetriable ? TryOpenWithRetry(null, overrides) : TryOpen(null, overrides)))
                     {
                         throw ADP.InternalError(ADP.InternalErrorCode.SynchronousConnectReturnedPending);

src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlConnection.cs

@@ -1350,6 +1350,7 @@ public override void Close()
                         _statistics._closeTimestamp = ADP.TimerCurrent();
                     }
                 }
+                // @TODO: CER Exception Handling was removed here (see GH#3581)
                 catch (Exception ex)
                 {
                     e = ex;

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/Diagnostics/SqlDiagnosticListener.cs

@@ -9,8 +9,6 @@
 #if NET
 using System.Reflection;
 using System.Runtime.Loader;
-#else
-using System.Runtime.ConstrainedExecution;
 #endif
 
 namespace Microsoft.Data.SqlClient.Diagnostics
@@ -487,7 +485,6 @@ public void WriteTransactionRollbackError(
         private void SqlDiagnosticListener_UnloadingAssemblyLoadContext(AssemblyLoadContext obj) =>
             Dispose();
 #else
-        [PrePrepareMethod]
         private void SqlDiagnosticListener_UnloadingAppDomain(object sender, EventArgs e) =>
             Dispose();
 #endif