Remove cancellation token from new System.Data CloseAsync() (#39070)

Affects DbDataReader and DbConnection, since these APIs are very likely
to be used for cleanup only, in which case a cancellation token is
an anti-pattern (similar to why DisposeAsync doesn't accept one).

See discussion here:
dotnet/standard#1283 (review)

Fixes #39069

src/System.Data.Common/ref/System.Data.Common.cs

@@ -1916,7 +1916,7 @@ public virtual event System.Data.StateChangeEventHandler StateChange { add { } r
         public abstract void ChangeDatabase(string databaseName);
         public virtual System.Threading.Tasks.Task ChangeDatabaseAsync(string databaseName, System.Threading.CancellationToken cancellationToken = default) { throw null; }
         public abstract void Close();
-        public virtual System.Threading.Tasks.Task CloseAsync(System.Threading.CancellationToken cancellationToken = default) { throw null; }
+        public virtual System.Threading.Tasks.Task CloseAsync() { throw null; }
         public System.Data.Common.DbCommand CreateCommand() { throw null; }
         protected abstract System.Data.Common.DbCommand CreateDbCommand();
         public virtual void EnlistTransaction(System.Transactions.Transaction transaction) { }
@@ -2062,7 +2062,7 @@ protected DbDataReader() { }
         public abstract int RecordsAffected { get; }
         public virtual int VisibleFieldCount { get { throw null; } }
         public virtual void Close() { }
-        public virtual System.Threading.Tasks.Task CloseAsync(System.Threading.CancellationToken cancellationToken = default) { throw null; }
+        public virtual System.Threading.Tasks.Task CloseAsync() { throw null; }
         [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
         public void Dispose() { }
         public virtual System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }

src/System.Data.Common/src/System/Data/Common/DbConnection.cs

@@ -88,13 +88,8 @@ public ValueTask<DbTransaction> BeginTransactionAsync(IsolationLevel isolationLe
 
         public abstract void Close();
 
-        public virtual Task CloseAsync(CancellationToken cancellationToken = default)
+        public virtual Task CloseAsync()
         {
-            if (cancellationToken.IsCancellationRequested)
-            {
-                return Task.FromCanceled(cancellationToken);
-            }
-
             try
             {
                 Close();

src/System.Data.Common/src/System/Data/Common/DbDataReader.cs

@@ -32,13 +32,8 @@ protected DbDataReader() : base() { }
 
         public virtual void Close() { }
 
-        public virtual Task CloseAsync(CancellationToken cancellationToken = default)
+        public virtual Task CloseAsync()
         {
-            if (cancellationToken.IsCancellationRequested)
-            {
-                return Task.FromCanceled(cancellationToken);
-            }
-
             try
             {
                 Close();