shuf: remove non-GNU --random-seed to avoid divergence of interfaces

[oech3]

This is essentially duplicated with --random-source and potentially corrupts scripts written with GNU coreutils.
Really bad extention. Closes #11157

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/follow-name (passes in this run but fails in the 'main' branch)