pointcache: Fix freeing all bakes in particle mode

Freeing all bakes didn't free edited cache in particle mode, this lead
to unresponsive ui and crashes.

Now use same logic as for freeing single bake.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54822 954f8c5b-7b00-dc11-b283-0030488c597c