Remove link from Memory<T>.ToArray() to itself (#2815)

Replace <xref=System.Memory%601.ToArray%2A> with `ToArray` as it is not enabled in Docs page.

Author: nogic1008

xml/System/Memory`1.xml

@@ -750,7 +750,7 @@ The garbage collector will not move the memory until the returned <xref:System.B
         <remarks>
           <format type="text/markdown"><![CDATA[  
 
-Because a call to the <xref=System.Memory%601.ToArray%2A> method performs a heap allocation, it should generally be avoided. However, it is sometimes necessary to take advantage of functionality that is only available for arrays.
+Because a call to the `ToArray` method performs a heap allocation, it should generally be avoided. However, it is sometimes necessary to take advantage of functionality that is only available for arrays.
 
 Each call to the `ToArray` method returns a new array. 
 
@@ -833,4 +833,4 @@ This method copies all of the contents of the current <xref:System.Memory%601> i
       </Docs>
     </Member>
   </Members>
-</Type>
+</Type>