fix(accoridon): remove unneeded card-title class

[7185]

This is only relevant with bs4.
You can see here that the headers are bigger than their bs3 counterparts and that the titles aren't vertically centered.
This is because of the card-title class which adds a margin under those titles. This class is actually used wrongly here since it serves other purposes: adding a style on <h*> elements in the panel itself (not the header). See the docs on Card Components.

[codecov]

Codecov Report

Merging #2024 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development    #2024   +/-   ##
============================================
  Coverage        86.54%   86.54%           
============================================
  Files               85       85           
  Lines             2252     2252           
  Branches           290      290           
============================================
  Hits              1949     1949           
  Misses             203      203           
  Partials           100      100

Impacted Files	Coverage Δ
src/accordion/accordion-group.component.ts	96.15% <ø> (ø)	⬆️

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[valorkin]

Thanks for great explanation!