Remove "Should not compile" directive from feature tests

Instead, let the Error directive determine if there are any expected
errors.
The 2 changes in this file are due to exposed issues. I should have included that in the description.

In this case the scanner accepted`"\u{123}"` even though the option was off. It lead to a runtime error when we finally evaled the code. That would of course change as soon as V8 lands its support for this syntax. If the option is off the parser should not support that option.