Remove Bootstrap 4's Cards class name from Epics

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

ee/app/views/shared/_epics.html.haml

-.card.card-without-border
-  %ul.content-list.issuable-list
+%ul.content-list.issuable-list
   = render partial: 'groups/epics/epic', collection: @epics
 
 = paginate_collection @epics

ee/changelogs/unreleased/289967-remove-bootstrap-4-s-cards-components-from-epics.yml

+---
+title: Remove Bootstrap 4's Cards class name from Epics
+merge_request: 48856
+author: Takuya Noguchi
+type: performance