Remove usage of Features from wasmtime::Config API (#763)

Instead expose a number of boolean accessors which doesn't require users
to construct a foreign `Features` type and allows us to decouple the API
of the `wasmtime` crate from the underlying implementation detail.

crates/misc/rust/src/lib.rs

@@ -6,7 +6,6 @@ pub mod __rt {
     pub use anyhow;
     pub use wasmtime;
     pub use wasmtime_interface_types;
-    pub use wasmtime_jit;
     pub use wasmtime_wasi;
 
     use std::convert::{TryFrom, TryInto};