remove duplicate import

src/lib.rs

@@ -41,7 +41,6 @@ pub use transaction::TransactionHandle;
 
 use allocator::{AllocatorState, GeneralPurposeAllocator, SlabListPointer, SlabPointer};
 use atomic_arc::AtomicArc;
-use mapped::ReaderTrait;
 use memmap::{Mmap, MmapMut};
 use zerocopy::{AsBytes, FromBytes, FromZeroes, Ref, Unaligned, LE};