Fix warnings

Author: bjorn3

src/base.rs

@@ -7,14 +7,12 @@ use gccjit::{
     GlobalKind,
 };
 use rustc_middle::dep_graph;
-use rustc_middle::middle::exported_symbols;
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::mir::mono::Linkage;
 use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
 use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
 use rustc_codegen_ssa::mono_item::MonoItemExt;
 use rustc_codegen_ssa::traits::DebugInfoMethods;
-use rustc_metadata::EncodedMetadata;
 use rustc_session::config::DebugInfo;
 use rustc_span::Symbol;