Revert "[AST] Build recovery expressions by default for C++."

This reverts commit 0788acbccbec094903a3425ffe5a98f8d55cbd64.
This reverts commit c2d7a1f79cedfc9fcb518596aa839da4de0adb69:  Revert "[clangd] Add test for FindTarget+RecoveryExpr (which already works). NFC"

It causes a crash on invalid code:

class X {
  decltype(unresolved()) foo;
};
constexpr int s = sizeof(X);
diff --git a/clang/unittests/Sema/CodeCompleteTest.cpp b/clang/unittests/Sema/CodeCompleteTest.cpp
index 5c8940c..a9441a6 100644
--- a/clang/unittests/Sema/CodeCompleteTest.cpp
+++ b/clang/unittests/Sema/CodeCompleteTest.cpp
@@ -487,7 +487,6 @@
     auto x = decltype(&1)(^);
     auto y = new decltype(&1)(^);
   )cpp";
-  EXPECT_THAT(collectPreferredTypes(Code),
-              Each("decltype(<recovery-expr>(1))"));
+  EXPECT_THAT(collectPreferredTypes(Code), Each("NULL TYPE"));
 }
 } // namespace