remove unnecessary files

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm/src/mem_table.rs

@@ -1,5 +1,3 @@
-#![allow(dead_code)] // REMOVE THIS LINE after fully implementing this functionality
-
 use std::ops::Bound;
 use std::path::Path;
 use std::sync::atomic::AtomicUsize;