Delete all* references to launcher clings.

Launcher clings are dead. Delete all the code and resources associated with
them.

* Did not delete the actual code the marks the cling as dismissed since it's
used in db upgrade and backup/restore paths. Figured we probably want to keep
that.

Change-Id: I28841b4a430187b62b239afeb64bee81a798e259
Fixes: 29461092