refactor: Remove new streaming old multiscan

[coastalwhite]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 85.86387% with 27 lines in your changes missing coverage. Please review.

Project coverage is 79.90%. Comparing base (5e51218) to head (0ad99df).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/plans/ir/scan_sources.rs	52.63%	18 Missing ⚠️
crates/polars-stream/src/nodes/io_sources/csv.rs	90.90%	8 Missing ⚠️
crates/polars-plan/src/plans/conversion/scans.rs	97.36%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21300      +/-   ##
==========================================
+ Coverage   79.82%   79.90%   +0.07%     
==========================================
  Files        1596     1596              
  Lines      228565   228595      +30     
  Branches     2608     2608              
==========================================
+ Hits       182462   182666     +204     
+ Misses      45507    45333     -174     
  Partials      596      596              

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