Removed duplicated function to create a swap fs

The mkfs() function in common/utils.py already can be used to create
a swap fs on a device, so there's no need to create another one in the
deploy_utils.py file.

Change-Id: I0e1983d53b43d69b350cff462e975984ce2d86c9
Merge "Removed duplicated function to create a swap fs"