a11y: Remove unnecessary vfunc impl
a11y: Remove unnecessary vfunc impl

atk has a default implementation that's identical.

jessevdk/vte,flaxandteal/gasket-vte,flaxandteal/gasket-vte,rvu95/vte,saitoha/vte-sixel,thestinger/vte-ng,rvu95/vte,jessevdk/vte,jessevdk/vte,saitoha/vte-sixel,thestinger/vte-ng,flaxandteal/gasket-vte,rvu95/vte,rvu95/vte,flaxandteal/gasket-vte,saitoha/vte-sixel,jessevdk/vte,thestinger/vte-ng