Remove bootloader naming logic for unsupported Python versions

[jrmccluskey]

The minimum Python version currently supported is 3.8, but there was some leftover logic in the Python boot.go script around wheel naming for versions 3.6 and 3.7. This change removes that unused logic.

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[codecov]

Codecov Report

Merging #28414 (fcbfb08) into master (8b2525b) will increase coverage by 0.00%.
Report is 62 commits behind head on master.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #28414    +/-   ##
========================================
  Coverage   72.33%   72.33%            
========================================
  Files         681      682     +1     
  Lines      100355   100541   +186     
========================================
+ Hits        72592    72728   +136     
- Misses      26189    26239    +50     
  Partials     1574     1574            

Flag	Coverage Δ
python	82.87% <ø> (-0.03%)	⬇️

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[tvalentyn]

Thanks!