We no longer need fpm

We are doing agent updates as gems.

[finishes #49812867]
Revert deb based agent update

* [#49035201]
* We will use gems to update agent for development
Rename file to match only task
Implicitly abort with sh and remove unused require
[#49035201] Introduce rake bosh_agent:update

* Quicker dev cycle
* Updates by building and publishing a new bosh_agent gem