After using the Purge Unused Data operator, hovering mouse over outliner
makes outliner tree dirty as the tree is not being rebuilt. The operator is
defined in python which calls `ANIM_armature_bonecoll_remove`. Add
notifier in that function code so that `outliner_main_region_listener`will tag
the outliner region for full redraw.
Pull Request: https://projects.blender.org/blender/blender/pulls/140256
0faf2a058e