Remove references to deprecated extern crate "foo" as bar syntax

This syntax was removed in b24a3b8 but references remained in the
grammar, the reference, rustdoc generation, and some auxiliary test
files that don't seem to have been used since 812637e.

src/librustdoc/html/render.rs

@@ -1643,7 +1643,7 @@ fn item_module(w: &mut fmt::Formatter, cx: &Context,
             clean::ExternCrateItem(ref name, ref src) => {
                 match *src {
                     Some(ref src) => {
-                        try!(write!(w, "<tr><td><code>{}extern crate \"{}\" as {};",
+                        try!(write!(w, "<tr><td><code>{}extern crate {} as {};",
                                     VisSpace(myitem.visibility),
                                     src,
                                     name))