auto merge of #13777 : lifthrasiir/rust/no-multi-viewitemuse, r=alexcrichton

It reflected the obsolete syntax `use a, b, c;` and did not make past the parser (though it was a non-fatal error so we can continue). This legacy affected many portions of rustc and rustdoc as well, so this PR cleans them up altogether.

As a side effect of cleanup, we now have `SCHEMA_VERSION` in `rustdoc::clean` (instead of the crate root), so it has a better chance to be updated when `rustdoc::clean` gets updated.

src/librustdoc/html/render.rs

@@ -1167,12 +1167,10 @@ fn item_module(w: &mut Writer, cx: &Context,
                         try!(write!(w, ";</code></td></tr>"));
                     }
 
-                    clean::Import(ref imports) => {
-                        for import in imports.iter() {
-                            try!(write!(w, "<tr><td><code>{}{}</code></td></tr>",
-                                          VisSpace(myitem.visibility),
-                                          *import));
-                        }
+                    clean::Import(ref import) => {
+                        try!(write!(w, "<tr><td><code>{}{}</code></td></tr>",
+                                      VisSpace(myitem.visibility),
+                                      *import));
                     }
                 }