remove wrong ISO section from safe navigation test; ref 4c1ce0f6

test/t/nil.rb

@@ -33,7 +33,7 @@ assert('NilClass#to_s', '15.2.4.3.5') do
   assert_equal '', nil.to_s
 end
 
-assert('safe navigation', '15.2.4.3.5') do
+assert('safe navigation') do
   assert_nil nil&.size
   assert_equal 0, []&.size
 end