UI tests cleanup
`@matthiaskrgr` noticed some `run-pass` annotations in some crash tests that were added in #3922. At that moment they seemed to be necessary to make the tests fail in case of an ICE, but they do not seem to be needed anymore. To test this I forced an ICE in a file with and without annotations, with and without stderr files, and the ICE makes the test fail every time.
In addition, I've applied a suggestion from `@ehuss` and `@jyn514` to add `emit=metadata` to the rustc flags for the UI tests. In my machine this improved the run time from ~17 to ~12 seconds.
changelog: none
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