release/azure: Don't use azure-agent deprovision to build image

Deprovision feature of waagent is used for preparing to capture a
running VM and turn it into a VM image. Using it in the process of
building a VM image from scratch will cause some side effects such as
the hostname of the building host getting reset.

Remove calling the deprovision command and use a simpler way to fulfill
the requirements of the Azure VM image.

Sponsored by: The FreeBSD Foundation