sim: Flatten 'area' module in mcuboot-sys

It isn't necessary for the 'area' module to be exposed.  Re-export the
two definitions from the crate at the top level, and make the module
private.

Signed-off-by: David Brown <david.brown@linaro.org>

sim/mcuboot-sys/src/lib.rs

@@ -2,6 +2,11 @@ extern crate libc;
 #[macro_use] extern crate log;
 extern crate simflash;
 
-pub mod area;
+mod area;
 pub mod c;
+
+// The API needs to be public, even though it isn't intended to be called by Rust code, but the
+// functions are exported to C code.
 pub mod api;
+
+pub use area::{AreaDesc, FlashId};

sim/src/main.rs

@@ -24,8 +24,7 @@ mod caps;
 mod tlv;
 
 use simflash::{Flash, SimFlash};
-use mcuboot_sys::area::{AreaDesc, FlashId};
-use mcuboot_sys::c;
+use mcuboot_sys::{c, AreaDesc, FlashId};
 use caps::Caps;
 use tlv::TlvGen;