cargo: Clean up serde dependencies

There is no need to include serde_derive separately,
as it can be specified as serde feature instead.

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

vmm/src/memory_manager.rs

@@ -17,6 +17,7 @@ use arch::{layout, RegionType};
 use devices::ioapic;
 #[cfg(target_arch = "x86_64")]
 use libc::{MAP_NORESERVE, MAP_POPULATE, MAP_SHARED, PROT_READ, PROT_WRITE};
+use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::convert::TryInto;
 use std::ffi;