a11y: Don't explicitly set accessible parent
a11y: Don't explicitly set accessible parent

Most other widget's a11y implementations don't do this either.

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