Fix warning.

Author: khuey

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -20,7 +20,7 @@ use rustc_session::config::{self, DebugInfo};
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
 use rustc_span::{
-    BytePos, Pos, SourceFile, SourceFileAndLine, SourceFileHash, Span, StableSourceFileId, DUMMY_SP,
+    BytePos, Pos, SourceFile, SourceFileAndLine, SourceFileHash, Span, StableSourceFileId,
 };
 use rustc_target::abi::Size;
 use smallvec::SmallVec;