Remove transitional XPath

[westonruter]

Summary

This removes the transitional XPath logic from #1797. This PR should only be merged after #1797 has been live for a few weeks. The logic was put in place so that the new XPath format wouldn't immediately invalidate all existing optimizations applied with old URL Metrics.

[github-actions]

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Co-authored-by: westonruter <[email protected]>

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.09%. Comparing base (b7c4475) to head (33d060a).
Report is 33 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk    #1820      +/-   ##
==========================================
+ Coverage   65.47%   66.09%   +0.62%     
==========================================
  Files          85       88       +3     
  Lines        6748     6851     +103     
==========================================
+ Hits         4418     4528     +110     
+ Misses       2330     2323       -7     

Flag	Coverage Δ
multisite	66.09% <100.00%> (+0.62%)	⬆️
single	38.78% <0.00%> (+0.90%)	⬆️

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