Clean up some code related to #[no_move].

The patch makes RootCollection a bit safer by making the StackRootTLS hold
it in place.

The use of no_move in CodeGenRust was leftover from when roots couldn't
be moved.

components/script/dom/bindings/codegen/CodegenRust.py

@@ -4927,7 +4927,6 @@ class CGDictionary(CGThing):
                        for m in self.memberInfo]
 
         return (string.Template(
-                "#[no_move]\n" +
                 "pub struct ${selfName} {\n" +
                 "${inheritance}" +
                 "\n".join(memberDecls) + "\n" +