Revert r291526: Re-enable /linkrepro test on Windows.

This broke the following two bots:

lld-x86_64-win7: the test failed because a diff command is not available
on that bot. That's a configuration error of the bot and will be fixed soon.

llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast: "tar xf" failed on that
bot. I suspect that it is due to the maximum path limitation on Windows.
A build directory contains a buildbot name, so it's longer than usual on
that machine. On Windows, many filesystem operations fail if a path is
longer than 255 characters. I'll try to address that in another patch.

llvm-svn: 291527