Remove Phobos dependency for deprecated symbols

[mihails-strasuns]

std.typetuple is pending deprecation in Phobos. To avoid failing
the test suite, DMD should not use those symbols by that time

This PR moves simplified type-only versions of that symbols to
unittest module itself

blocks dlang/phobos#3128

[mihails-strasuns]

What has happened with auto-teser? I can't see the log anymore.

[MartinNowak]

What has happened with auto-teser? I can't see the log anymore.

Yeah, something is broken, I already mailed Brad.

[MartinNowak]

Except for the regression tests this should be deleted. There is no use in duplicating phobos unittests in dmd.

[mihails-strasuns]

With proposed slower transition which does not deprecate std.typetuple initially there is no need in this PR.

I have no idea why it needs to use Phobos but looks like it checks the behaviour of built-in variadic lists. I guess that should be replaced with something more simple, not just removed?

[mihails-strasuns]

Ok, I refocused this to simply clean up variadic.d test - it indeed looks like a rather bad chunk of legacy that duplicated Phobos tests in bad way.

[mihails-strasuns]

Green. Is that what you wanted @MartinNowak ?

[mihails-strasuns]

Ping. This should be trivial to merge and it blocks Phobos PR.

[MartinNowak]

Auto-merge toggled on

[MartinNowak]

Now you removed anything phobos related not just std.typetuple, but should be OK.

[mihails-strasuns]

Now you removed anything phobos related not just std.typetuple

Yes, this was intentional. Otherwise it will strike back again if any other used Phobos symbol will get deprecated. DMD tests shouldn't rely on Phobos.