Remove std feature from cranelift-entity

cranelift/entity/src/list.rs

@@ -3,7 +3,7 @@ use crate::packed_option::ReservedValue;
 use crate::EntityRef;
 use core::marker::PhantomData;
 use core::mem;
-use std::vec::Vec;
+use alloc::vec::Vec;
 
 /// A small list of entity references allocated from a pool.
 ///