buffer: remove unused param from copyActual

[gurgunday]

Follow up to #61721

We added this quirky parameter in #60399 when implementing an optimization to Buffer.concat and Buffer.copy with the intention of eventually removing it when .concat used TypedArrayPrototypeSet in all cases

The parameter was only used in one place until it was removed in #61721:

https://github.com/nodejs/node/pull/61721/changes#diff-3c2cd5c512dd026a7765b6b2ae3f85785d3b7ea3795e11949892b7b73beee630L635

[richardlau]

This change is being made as part of #62032.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.64%. Comparing base (6a3d358) to head (ce5f8c4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62042      +/-   ##
==========================================
+ Coverage   89.58%   89.64%   +0.06%     
==========================================
  Files         674      676       +2     
  Lines      205159   206240    +1081     
  Branches    39352    39506     +154     
==========================================
+ Hits       183792   184894    +1102     
+ Misses      13583    13465     -118     
- Partials     7784     7881      +97     

Files with missing lines	Coverage Δ
lib/buffer.js	99.16% <100.00%> (ø)

... and 129 files with indirect coverage changes

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