[Issue 20180] Deprecated unittests should not be deprecated functions

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20180

--- Comment #1 from FeepingCreature <default_357-line at yahoo.de> ---
(This issue has come up in dmd nightly because deprecations from nested
functions and mixins used to be ignored, which allowed unit-threaded to work
without complaint.)

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