[compiler] Remove dangerous language mode accessors.

src/crankshaft/x64/lithium-codegen-x64.h

Index: src/crankshaft/x64/lithium-codegen-x64.h
diff --git a/src/crankshaft/x64/lithium-codegen-x64.h b/src/crankshaft/x64/lithium-codegen-x64.h
index 139645e6cdf806bf1dbc6f691f615d0088224cb7..f643e2b7ddc78d39ea190963c50cdc822029c14a 100644
--- a/src/crankshaft/x64/lithium-codegen-x64.h
+++ b/src/crankshaft/x64/lithium-codegen-x64.h
@@ -111,8 +111,6 @@ class LCodeGen: public LCodeGenBase {
 #undef DECLARE_DO
 
  private:
-  LanguageMode language_mode() const { return info()->language_mode(); }
-
   LPlatformChunk* chunk() const { return chunk_; }
   Scope* scope() const { return scope_; }
   HGraph* graph() const { return chunk()->graph(); }