chore: drop support for md.style

[yufeih]

md.style was introduced a while back to enforce some limited style guides on markdown files. The rulesets are limited to tags and does not meet many expectations of a markdown linter.

This PR drops support for md.style, in favor of many great alternative markdown linting tools such as markdownlint.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.15 ⚠️

Comparison is base (a3c8409) 76.86% compared to head (7ef6192) 76.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8973      +/-   ##
==========================================
- Coverage   76.86%   76.71%   -0.15%     
==========================================
  Files         601      592       -9     
  Lines       24968    24743     -225     
==========================================
- Hits        19191    18982     -209     
+ Misses       5777     5761      -16     

Impacted Files	Coverage Δ
...ild.ConceptualDocuments/BuildConceptualDocument.cs	87.87% <100.00%> (ø)
src/Docfx.Build.Engine/HostService.cs	73.72% <100.00%> (+0.55%)	⬆️
...ild.SchemaDriven/Processors/MarkdownInterpreter.cs	92.85% <100.00%> (ø)
src/Docfx.MarkdigEngine/MarkdigMarkdownService.cs	86.81% <100.00%> (-0.43%)	⬇️

... and 3 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.