Remove unused smallvec dependency

Author: dschoepe

source/rust_verify/src/lib.rs

@@ -28,7 +28,6 @@ extern crate rustc_session;
 extern crate rustc_span;
 extern crate rustc_trait_selection;
 extern crate rustc_type_ir;
-extern crate smallvec;
 
 mod attributes;
 mod buckets;