refactor(rust): Remove old streaming flag if we're going into new streaming

[orlp]

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[codecov]

Codecov Report

Attention: Patch coverage is 10.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 79.90%. Comparing base (37a492e) to head (b97f06c).
Report is 49 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/skeleton.rs	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18438      +/-   ##
==========================================
- Coverage   79.92%   79.90%   -0.03%     
==========================================
  Files        1495     1496       +1     
  Lines      200279   200200      -79     
  Branches     2867     2867              
==========================================
- Hits       160081   159977     -104     
- Misses      39652    39677      +25     
  Partials      546      546              

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