Remove a redundant "unsafe" specifier

src/history.rs

@@ -1348,10 +1348,8 @@ impl HistoryImpl {
     ///
     /// `fd` must be a valid argument to `flock(2)` with `LOCK_UN`.
     unsafe fn unlock_file(file: &mut File) {
-        unsafe {
         libc::flock(file.as_raw_fd(), LOCK_UN);
     }
-    }
 }
 
 // Returns the fd of an opened temporary file, or None on failure.