Revert "PR42587: diagnose unexpanded uses of a pack parameter of a generic" due to buildbot breakage.

This reverts commit r369722.

llvm-svn: 369725
diff --git a/clang/lib/Sema/SemaTemplateVariadic.cpp b/clang/lib/Sema/SemaTemplateVariadic.cpp
index b766e3c..f90bff6 100644
--- a/clang/lib/Sema/SemaTemplateVariadic.cpp
+++ b/clang/lib/Sema/SemaTemplateVariadic.cpp
@@ -313,17 +313,10 @@
 
     if (auto *LSI = dyn_cast<sema::LambdaScopeInfo>(Func)) {
       if (N == FunctionScopes.size()) {
-        const DeclContext *LambdaDC = LSI->CallOperator;
-        // While we're parsing the lambda-declarator, we don't have a call
-        // operator yet and the parameters instead get temporarily attached
-        // to the translation unit.
-        if (!LambdaDC)
-          LambdaDC = Context.getTranslationUnitDecl();
-
         for (auto &Pack : Unexpanded) {
           auto *VD = dyn_cast_or_null<VarDecl>(
               Pack.first.dyn_cast<NamedDecl *>());
-          if (VD && VD->getDeclContext() == LambdaDC)
+          if (VD && VD->getDeclContext() == LSI->CallOperator)
             LambdaParamPackReferences.push_back(Pack);
         }
       }