Remove rustc's std copy

[Zoxc]

This removes rustc's std copy if we're statically linking std into rustc_driver. This copy is not needed after #122362.

try-job: dist-x86_64-linux
try-job: dist-x86_64-msvc

[rustbot]

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[Kobzol]

Could you please comment this line in this PR, to enable post-optimization tests in the x64 Linux dist runner? Then we can try the dist tests in try builds.

[lqd]

This PR is still a WIP in order to run tests/debug/try alternatives on builders, right? As it currently looks like dd3f757 which failed in the previous PR.

[Zoxc]

I haven't tracked down the reason for the test failure yet. Does post-optimization tests specify the final binary as stage0-sysroot? Then runs tests as stage0 with a new std build?

[Kobzol]

Yeah, post-optimization tests essentially take the sysroot created in the dist step, and try to run tests with it (using the "allow stage0 sysroot" hack). It is implemented here.

[Kobzol]

It seems like this could progress after #129941. I tried it locally and we can remove the stage != "0" check and do this. And then see what tests break :)