Fix some warnings

src/memory/bump.rs

@@ -43,6 +43,7 @@ impl BumpAllocator {
 }
 
 impl FrameAllocator for BumpAllocator {
+    #[allow(unused)]
     fn set_noncore(&mut self, noncore: bool) {}
     
     fn free_frames(&self) -> usize {

src/memory/recycle.rs

@@ -5,7 +5,7 @@ use collections::Vec;
 
 use paging::PhysicalAddress;
 
-use super::{Frame, FrameAllocator, MemoryArea, MemoryAreaIter};
+use super::{Frame, FrameAllocator};
 
 pub struct RecycleAllocator<T: FrameAllocator> {
     inner: T,