go1: fix old reference to Sys method

The example was fixed; the simplifying rewrite was missed.

R=golang-dev
CC=golang-dev
https://golang.org/cl/5651080

doc/go1.html

@@ -1461,7 +1461,7 @@ the i-number expression could be contracted to
 </p>
 
 <pre>
-    fi.(*os.FileStat).Sys.(*syscall.Stat_t).Ino
+    fi.Sys().(*syscall.Stat_t).Ino
 </pre>
 
 <p>

doc/go1.tmpl

@@ -1364,7 +1364,7 @@ the i-number expression could be contracted to
 </p>
 
 <pre>
-    fi.(*os.FileStat).Sys.(*syscall.Stat_t).Ino
+    fi.Sys().(*syscall.Stat_t).Ino
 </pre>
 
 <p>