doc: fix wiki codelab title and srcextract.go

R=r, rsc1
CC=golang-dev
https://golang.org/cl/1953048

doc/codelab/wiki/index.html

-<div class="content">
-
-<h1>Writing Web Applications</h1>
-
+<!-- Codelab: Writing Web Applications -->
 <h2>Introduction</h2>
 
 <p>
@@ -996,5 +993,3 @@ Here are some simple tasks you might want to tackle on your own:
 	(hint: you could use <code>regexp.ReplaceAllFunc</code> to do this)
 	</li>
 </ul>
-
-</div>

doc/codelab/wiki/srcextract.go

@@ -25,7 +25,7 @@ func main() {
 		os.Exit(2)
 	}
 	// load file
-	file, err := parser.ParseFile(*srcFn, nil, nil, 0)
+	file, err := parser.ParseFile(*srcFn, nil, 0)
 	if err != nil {
 		log.Exit(err)
 	}

doc/codelab/wiki/wiki.html

-<div class="content">
-
-<h1>Writing Web Applications</h1>
-
+<!-- Codelab: Writing Web Applications -->
 <h2>Introduction</h2>
 
 <p>
@@ -782,5 +779,3 @@ Here are some simple tasks you might want to tackle on your own:
 	(hint: you could use <code>regexp.ReplaceAllFunc</code> to do this)
 	</li>
 </ul>
-
-</div>