docs: Remove obsolete config, and invalid doc markup

[paulgessinger]

This starts throwing warnings in Doxygen 1.9.5.

[codecov]

Codecov Report

Merging #1519 (5b36ffc) into main (91a1e87) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1519   +/-   ##
=======================================
  Coverage   48.59%   48.59%           
=======================================
  Files         381      381           
  Lines       20650    20650           
  Branches     9475     9475           
=======================================
  Hits        10034    10034           
  Misses       4064     4064           
  Partials     6552     6552           

Impacted Files	Coverage Δ
...Acts/Vertexing/AdaptiveGridDensityVertexFinder.hpp	80.00% <ø> (ø)
...clude/Acts/Vertexing/AdaptiveMultiVertexFinder.hpp	78.57% <ø> (ø)
...clude/Acts/Vertexing/AdaptiveMultiVertexFitter.hpp	72.00% <ø> (ø)
...include/Acts/Vertexing/FullBilloirVertexFitter.hpp	66.66% <ø> (ø)
...include/Acts/Vertexing/GridDensityVertexFinder.hpp	80.00% <ø> (ø)
...e/include/Acts/Vertexing/IterativeVertexFinder.hpp	82.35% <ø> (ø)
...nclude/Acts/Vertexing/TrackDensityVertexFinder.hpp	75.00% <ø> (ø)
Core/include/Acts/Vertexing/ZScanVertexFinder.hpp	81.81% <ø> (ø)

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