Fix [#34005] blender will close immediately in debug mode on deleting objects

Was silly mistake from rigidbody merge, base was used after it's been
freed.

Now don't free base in BKE_scene_base_remove() and rename it to
BKE_scene_base_unlink().

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54110 954f8c5b-7b00-dc11-b283-0030488c597c