Use proper scaling for vertical shift of bevelled fractions. (mathjax/MathJax#3506)

[dpvc]

This PR fixes a problem with CHTML output for bevelled fractions. The vertical positions were not using the proper scaling factor (the data from getBevelledData() includes the scaling already, so we don't need to adjust for it).

Resolves issue mathjax/MathJax#3506.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.51%. Comparing base (95faa0c) to head (2b04e5a).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
ts/output/chtml/Wrappers/mfrac.ts	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop    #1419     +/-   ##
==========================================
  Coverage    86.51%   86.51%             
==========================================
  Files          340      340             
  Lines        85993    85993             
  Branches      4825     3184   -1641     
==========================================
  Hits         74397    74397             
  Misses       11596    11596             

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[zorkow]

lgtm.