Drop the "-rust" from the "libsignal-protocol" crate

The project corresponds to libsignal-protocol-java and the others, but
/within/ the language we don't need to tag with the language name.

rust/protocol/tests/session.rs

@@ -6,7 +6,7 @@
 mod support;
 
 use futures::executor::block_on;
-use libsignal_protocol_rust::*;
+use libsignal_protocol::*;
 use rand::rngs::OsRng;
 use std::convert::TryFrom;
 use support::*;