ART: Even more Quick cleanup

Remove Backend.

Change-Id: I247cc65ccda6a362ba1a8f5e73e7f12ecd980a87
diff --git a/compiler/dex/compiler_ir.h b/compiler/dex/compiler_ir.h
index e7182a9..51c4a43 100644
--- a/compiler/dex/compiler_ir.h
+++ b/compiler/dex/compiler_ir.h
@@ -29,9 +29,9 @@
 
 namespace art {
 
-class Backend;
 class ClassLinker;
 class CompilerDriver;
+class Mir2Lir;
 class MIRGraph;
 
 struct CompilationUnit {
@@ -66,7 +66,7 @@
   ArenaStack arena_stack;  // Arenas for ScopedArenaAllocator.
 
   std::unique_ptr<MIRGraph> mir_graph;   // MIR container.
-  std::unique_ptr<Backend> cg;           // Target-specific codegen.
+  std::unique_ptr<Mir2Lir> cg;           // Target-specific codegen.
   TimingLogger timings;
   bool print_pass;                 // Do we want to print a pass or not?