Remove vector manipulation from demo project

The vector support needs to be covered by our test suite, but it doesn't
need to be featured to this extent in our intro code.
diff --git a/demo-rs/src/main.rs b/demo-rs/src/main.rs
index 8bf9926..66dfc79 100644
--- a/demo-rs/src/main.rs
+++ b/demo-rs/src/main.rs
@@ -6,19 +6,13 @@
         x: UniquePtr<ThingC>,
     }
 
-    struct JsonBlob {
-        json: UniquePtr<CxxString>,
-        blob: UniquePtr<Vector<u8>>,
-    }
-
     extern "C" {
         include!("demo-cxx/demo.h");
 
         type ThingC;
         fn make_demo(appname: &str) -> UniquePtr<ThingC>;
         fn get_name(thing: &ThingC) -> &CxxString;
-        fn do_thing(state: SharedThing) -> UniquePtr<Vector<u8>>;
-        fn get_jb(v: &Vec<u8>) -> JsonBlob;
+        fn do_thing(state: SharedThing);
     }
 
     extern "Rust" {
@@ -37,24 +31,9 @@
     let x = ffi::make_demo("demo of cxx::bridge");
     println!("this is a {}", ffi::get_name(x.as_ref().unwrap()));
 
-    let vec = ffi::do_thing(ffi::SharedThing {
+    ffi::do_thing(ffi::SharedThing {
         z: 222,
         y: Box::new(ThingR(333)),
         x,
     });
-
-    println!("vec length = {}", vec.as_ref().unwrap().size());
-    for (i, v) in vec.as_ref().unwrap().into_iter().enumerate() {
-        println!("vec[{}] = {}", i, v);
-    }
-
-    let mut rv: Vec<u8> = Vec::new();
-    for _ in 0..1000 {
-        rv.push(33);
-    }
-    let jb = ffi::get_jb(&rv);
-    println!("json: {}", jb.json.as_ref().unwrap());
-    for (i, v) in jb.blob.as_ref().unwrap().into_iter().enumerate() {
-        println!("jb.blob[{}] = {}", i, v);
-    }
 }