[dotnet] Revert deprecation of GetAttribute method (#14956)

Author: nvborisenko

dotnet/src/support/Events/EventFiringWebDriver.cs

@@ -1613,7 +1613,6 @@ public void Click()
             /// </summary>
             /// <param name="attributeName">Attribute you wish to get details of</param>
             /// <returns>The attribute's current value or null if the value is not set.</returns>
-            [Obsolete("Use GetDomAttribute(string attributeName) or GetDomProperty(string propertyName). GetAttribute(string attributeName) will be removed in Selenium 6.")]
             public string GetAttribute(string attributeName)
             {
                 string attribute = string.Empty;

dotnet/src/webdriver/IWebElement.cs

@@ -172,7 +172,6 @@ public interface IWebElement : ISearchContext
         /// </list>
         /// </remarks>
         /// <exception cref="StaleElementReferenceException">Thrown when the target element is no longer valid in the document DOM.</exception>
-        [Obsolete("Use GetDomAttribute(string attributeName) or GetDomProperty(string propertyName). GetAttribute(string attributeName) will be removed in Selenium 6.")]
         string GetAttribute(string attributeName);
 
         /// <summary>

dotnet/src/webdriver/WebElement.cs

@@ -411,7 +411,6 @@ public virtual ReadOnlyCollection<IWebElement> FindElements(string mechanism, st
         /// via JavaScript.
         /// </remarks>
         /// <exception cref="StaleElementReferenceException">Thrown when the target element is no longer valid in the document DOM.</exception>
-        [Obsolete("Use GetDomAttribute(string attributeName) or GetDomProperty(string propertyName). GetAttribute(string attributeName) will be removed in Selenium 6.")]
         public virtual string GetAttribute(string attributeName)
         {
             Response commandResponse = null;