Remove SearchList from Matchless

[johnynek]

with #1299 we don't need to have separate searchList code in each backend, just use WhileExpr.

[codecov]

Codecov Report

Attention: Patch coverage is 76.00000% with 18 lines in your changes missing coverage. Please review.

Project coverage is 89.52%. Comparing base (04a0e87) to head (45c7c0f).
Report is 110 commits behind head on main.

Files with missing lines	Patch %	Lines
...re/src/main/scala/org/bykn/bosatsu/Matchless.scala	68.96%	9 Missing ⚠️
...cala/org/bykn/bosatsu/codegen/clang/ClangGen.scala	70.00%	6 Missing ⚠️
...main/scala/org/bykn/bosatsu/MatchlessToValue.scala	80.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1300      +/-   ##
==========================================
- Coverage   91.32%   89.52%   -1.81%     
==========================================
  Files          96      106      +10     
  Lines       11846    13302    +1456     
  Branches     2675     3055     +380     
==========================================
+ Hits        10818    11908    +1090     
- Misses       1028     1394     +366     

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