Clarify return value for HttpHeaders#Remove(String) (dotnet#7402)

Author: bramhaag

xml/System.Net.Http.Headers/HttpHeaders.xml

@@ -414,7 +414,9 @@ New line characters in header values must be followed by a white-space character
       <Docs>
         <param name="name">The name of the header to remove from the collection.</param>
         <summary>Removes the specified header from the <see cref="T:System.Net.Http.Headers.HttpHeaders" /> collection.</summary>
-        <returns>Returns <see cref="T:System.Boolean" />.</returns>
+        <returns>
+          <see langword="true" /> if <paramref name="name" /> is successfully removed; otherwise, <see langword="false" />.  This method also returns <see langword="false" /> if <paramref name="item" /> was not found in the <see cref="T:System.Net.Http.Headers.HttpHeaders" /> collection or if <paramref name="item" /> is <see langword="null" />.
+        </returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>