sim: Switch to bitflags from enumflags

The bitflags crate seems to be better supported, and doesn't have the
problems getting the results back into the enum type.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/src/main.rs b/sim/src/main.rs
index 614def3..89be7ff 100644
--- a/sim/src/main.rs
+++ b/sim/src/main.rs
@@ -1,8 +1,7 @@
 #[macro_use] extern crate log;
 extern crate ring;
 extern crate env_logger;
-extern crate enumflags;
-#[macro_use] extern crate enumflags_derive;
+#[macro_use] extern crate bitflags;
 extern crate docopt;
 extern crate libc;
 extern crate rand;