Drop blockers from x11-themes/gnome-icon-theme-symbolic

Fixes #7 in Heather/gentoo-gnome

gnome-icon-theme-symbolic had blockers on gnome-power-manager-3.0* and
gnome-power-manager-3.1*. None of this stuff is in the tree any more,
and the latter blocker is clashing with gnome-power-manager-3.10.