Stop using "rlib"

I don't know if this matters at all, but I don't think we should use "rlib".
The [rust docs](https://doc.rust-lang.org/reference/linkage.html) suggest using "lib" by default.
"lib" probably just aliases to "rlib", but it lets the compiler pick what it wants.

platform/Cargo.toml

@@ -15,7 +15,7 @@ codegen-units = 1
 [lib]
 name = "host"
 path = "src/lib.rs"
-crate-type = ["staticlib", "rlib"]
+crate-type = ["staticlib", "lib"]
 
 [[bin]]
 name = "host"