audio/gnome-podcasts: drop unused distfile after a160015b86be

Previously, gettext-sys was listed more than once in order
to trigger the following logic in USES=cargo

.if ${_CARGO_CRATES:Mgettext-sys}
CARGO_ENV+= GETTEXT_BIN_DIR=${LOCALBASE}/bin \

		GETTEXT_INCLUDE_DIR=${LOCALBASE}/include \
		GETTEXT_LIB_DIR=${LOCALBASE}/lib

.endif