quic: remove obsolete setOutbound()

[efekrskl]

QuicStream.setOutbound() is an undocumented, untested predecessor to setBody(). It's not used anywhere in the codebase, and bypasses the enforced mutual exclusion with stream.writer.

[nodejs-github-bot]

Review requested:

• @nodejs/quic

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.45%. Comparing base (38a5f10) to head (2c6c2d5).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66646      +/-   ##
==========================================
- Coverage   90.45%   90.45%   -0.01%     
==========================================
  Files         791      791              
  Lines      276816   276797      -19     
  Branches    53197    53187      -10     
==========================================
- Hits       250403   250373      -30     
- Misses      16822    16834      +12     
+ Partials     9591     9590       -1     

Files with missing lines	Coverage Δ
lib/internal/quic/quic.js	100.00% <ø> (ø)

... and 29 files with indirect coverage changes

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