remove clone from job object

[ghostsquad]

https://github.com/ghostsquad/swarmci/blob/master/swarmci/job.py#L37

"Clone" should be just another "task", and should not be special. Example, of someone needs to first clone the repo:

tasks:
  - git clone ....
  - something else

Right now, clone isn't even implemented. So this is to suggest that the functionality should not be implemented.