Revert "Add extension to always default-initialize nullptr_t."

This reverts commit 46efdf2ccc2a80aefebf8433dbf9c7c959f6e629.

Richard Smith commented just after I submitted this that this is the
wrong solution.  Reverting so that I can fix differently.

llvm-svn: 349206
diff --git a/clang/test/SemaCXX/ast-print-crash.cpp b/clang/test/SemaCXX/ast-print-crash.cpp
index 33edc34..c108f66 100644
--- a/clang/test/SemaCXX/ast-print-crash.cpp
+++ b/clang/test/SemaCXX/ast-print-crash.cpp
@@ -7,6 +7,6 @@
 
 // CHECK:      struct {
 // CHECK-NEXT: } dont_crash_on_syntax_error;
-// CHECK-NEXT: decltype(nullptr) p(/*implicit*/(decltype(nullptr))0);
+// CHECK-NEXT: decltype(nullptr) p;
 struct {
 } dont_crash_on_syntax_error /* missing ; */ decltype(nullptr) p;