fix(bench): drop stress-ng benchmarks

The local 'CodSpeed Benchmarks' job kept hitting its job timeout on the
stress-ng rows. stress-ng is the only forking workload in the suite and
deadlocks under 'callgrind --trace-children=yes' on a lost pause() wakeup.

Root cause is an application-level race in stress-ng, not our code and not
a Valgrind signal-delivery bug. Its termination wait

    while (stress_continue(args))
        (void)shim_pause();

can miss the SIGALRM that clears the continue flag if the signal lands
between the flag check and pause(), so pause() blocks on a signal that
already arrived. stress-ng's alarm(1) re-alarm mitigation fails here because
alarm() is per-process (a forked worker that already lost its SIGALRM has no
self-armed alarm) and Valgrind serializes all guest threads onto one
scheduler lock, widening the check->pause() window from nanoseconds to
milliseconds. It reproduces on stock upstream Valgrind 3.26.0/3.25.1 too; the
only thing special about 'local' is that it is slower and runs extra configs,
so it trips the race far more often.

In practice only the full-* configs (--trace-children + cache-sim, the
slowest) hang; take_strings/echo/python3 are unaffected. stress-ng adds
little value as a callgrind throughput benchmark, so remove it rather than
work around an upstream bug. The 'timeout --kill-after=10s 120s' wrapper from
the previous commit stays as a backstop. (--fair-sched=yes was tried and
regressed the hang onto take_strings full-with-inline, so it was reverted.)

Author: not-matthias

bench/generate_config.py

@@ -22,8 +22,6 @@
     "testdata/take_strings-aarch64 varbinview_non_null",
     "echo Hello, World!",
     "python3 testdata/test.py",
-    "stress-ng --cpu 1 --cpu-ops 10",
-    "stress-ng --cpu 4 --cpu-ops 10",
 ]
 
 # Callgrind configurations: (extra args, config name, requires_codspeed). The