Revert "[Support][ErrorOr] Add support for convertable types."

This reverts commit a33e1fafac.

This unit test crashes on Darwon. It needs to be temporarily reverted
to unblock the test infrastructure.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174458 91177308-0d34-0410-b5e6-96231b3b80d8

unittests/Support/ErrorOrTest.cpp

@@ -53,17 +53,6 @@ TEST(ErrorOr, Types) {
   EXPECT_EQ(3, **t3());
 #endif
 }
-
-struct B {};
-struct D : B {};
-
-TEST(ErrorOr, Covariant) {
-  ErrorOr<B*> b(ErrorOr<D*>(0));
-
-#if LLVM_HAS_CXX11_STDLIB
-  ErrorOr<std::unique_ptr<B> > b1(ErrorOr<std::unique_ptr<D> >(0));
-#endif
-}
 } // end anon namespace
 
 struct InvalidArgError {