only use #[no_core] in libcore

src/libsyntax/ext/pipes/ast_builder.rs

@@ -13,8 +13,6 @@
 // To start with, it will be use dummy spans, but it might someday do
 // something smarter.
 
-use core::prelude::*;
-
 use abi::AbiSet;
 use ast::ident;
 use ast;
@@ -26,8 +24,6 @@ use ext::quote::rt::*;
 use opt_vec;
 use opt_vec::OptVec;
 
-use core::vec;
-
 // Transitional reexports so qquote can find the paths it is looking for
 mod syntax {
     pub use ext;