Fix various build warnings

This should remove six separate warnings when building servo. One of
the warnings was an unused mut, and the other were various dead code
warnings

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

@@ -1850,6 +1850,7 @@ class CGImports(CGWrapper):
                 'unused_imports',
                 'unused_variables',
                 'unused_assignments',
+                'unused_mut',
             ]
 
         def componentTypes(type):

components/script/dom/dissimilaroriginlocation.rs

@@ -45,6 +45,7 @@ impl DissimilarOriginLocation {
                            DissimilarOriginLocationBinding::Wrap)
     }
 
+    #[allow(dead_code)]
     pub fn origin(&self) -> &MutableOrigin {
         self.window.origin()
     }

components/script/dom/dissimilaroriginwindow.rs

@@ -65,6 +65,7 @@ impl DissimilarOriginWindow {
         unsafe { DissimilarOriginWindowBinding::Wrap(cx, win) }
     }
 
+    #[allow(dead_code)]
     pub fn origin(&self) -> &MutableOrigin {
         self.globalscope.origin()
     }

components/script/dom/location.rs

@@ -61,6 +61,7 @@ impl Location {
         self.window.load_url(self.get_url(), true, true, None);
     }
 
+    #[allow(dead_code)]
     pub fn origin(&self) -> &MutableOrigin {
         self.window.origin()
     }