Remove incorrect "unique" claim from ShortestDayNames documentation

Co-authored-by: tarekgh <[email protected]>

Author: Copilot

xml/System.Globalization/DateTimeFormatInfo.xml

@@ -2828,7 +2828,7 @@ This property is affected if the value of the <xref:System.Globalization.DateTim
         <ReturnType>System.String[]</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Gets or sets a string array of the shortest unique abbreviated day names associated with the current <see cref="T:System.Globalization.DateTimeFormatInfo" /> object.</summary>
+        <summary>Gets or sets a string array of the shortest abbreviated day names associated with the current <see cref="T:System.Globalization.DateTimeFormatInfo" /> object.</summary>
         <value>A string array of day names.</value>
         <remarks>
           <format type="text/markdown"><![CDATA[