Revert "jailer: Use O_NOFOLLOW for cgroup and netns file operations" - #5959

This reverts commit ce2a467.

It turns out users do want to legitimately use symlinks in these paths. Commit 72340ca ("docs: Clarify that all jailer inputs must be trusted") updated documentation to make it clear that all jailer inputs are always considered trusted anyway, so this revert is not a regression.

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