chore: remove PY3 conditional logic

[mistercrunch]

CATEGORY

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• Bug Fix
• Enhancement (new features, refinement)
• Refactor
• Add tests
• Build / Development Environment
• Documentation

SUMMARY

Remove Python 3 conditional logic

[codecov-io]

Codecov Report

Merging #8149 into master will decrease coverage by <.01%.
The diff coverage is 83.33%.

@@            Coverage Diff            @@
##           master   #8149      +/-   ##
=========================================
- Coverage    66.2%   66.2%   -0.01%     
=========================================
  Files         479     479              
  Lines       22936   22930       -6     
  Branches     2524    2524              
=========================================
- Hits        15184   15180       -4     
+ Misses       7618    7616       -2     
  Partials      134     134

Impacted Files	Coverage Δ
superset/utils/core.py	88.05% <83.33%> (+0.21%)	⬆️

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