Remove non-existent setsidaccept4 syscall from seccomp allowlist

[vitkyrka]

Summary

• setsidaccept4 is not a real Linux syscall — it appears to be a typo where setsid and accept4 were accidentally concatenated when the seccomp profile was first added in eb3cc9e
• Both setsid and accept4 already appear correctly as separate entries in DefaultSyscallsForSystemProbe()
• This removes the phantom entry so the seccomp allowlist matches only real syscalls

Test plan

• Verify setsidaccept4 does not appear in /usr/include/asm/unistd.h or any Linux syscall table (it doesn't)
• Confirm accept4 (line 97) and setsid (line 257) remain in the list

🤖 Generated with Claude Code

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.76%. Comparing base (540be47) to head (27579c8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2992      +/-   ##
==========================================
- Coverage   40.76%   40.76%   -0.01%     
==========================================
  Files         332      332              
  Lines       28198    28197       -1     
==========================================
- Hits        11495    11494       -1     
  Misses      15928    15928              
  Partials      775      775              

Flag	Coverage Δ
unittests	40.76% <ø> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
...controller/datadogagent/component/agent/default.go	44.21% <ø> (-0.08%)	⬇️

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[datadog-datadog-prod-us1-2]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 41.07% (-0.00%)

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