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

This reverts commit 0788acbc.
This reverts commit c2d7a1f7:  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);