Removing field _isReleasingDataSource

Author: LeafShi1

src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridView.cs

@@ -346,7 +346,6 @@ private const DataGridViewAutoSizeRowCriteriaInternal InvalidDataGridViewAutoSiz
     private int _inBulkPaintCount;
     private int _inBulkLayoutCount;
     private int _inPerformLayoutCount;
-    private bool _isReleasingDataSource;
 
     private int _keyboardResizeStep;
     private Rectangle _resizeClipRectangle;