Remove all vumi related code

This is all hosted externally now and unused internally.

We might want to figure out if we should add ::decomission code
to kill the things that were running, or do that manually on
silver.

This also removes most unmodularized code under 'mobile/', so
yay

Change-Id: I56746045a53a6f8c2f9e7e41c0fceecf17943373