PHUIPropertyListView defines setHasKeyboardShortcuts() using AphrontKeyboardShortcutsAvailableView setting the CSS class keyboard-shortcuts-available defined in phui-property-list-view.css and phui-property-list-view.css, the latter being the only consumer of the icon key_question.png.
Searching the codebase for asKeyboardShortcuts there are zero callers as src/applications/differential/view/DifferentialRevisionDetailView.php got deleted in https://we.phorge.it/rP148a50e48be146b88036032d1cad772d2627da28. Thus remove that unused code/files.
Note that this is unrelated to setEnableKeyboardShortcuts() in PHUIPagerView.