Add remove_machine method to Lab class

[tcaiazzi]

Currently, there is no straightforward way to remove a device from a network scenario. Users are required to manually:

1. Delete the device from the machines list.
2. Detach it from all collision domains it is connected to.
3. (Eventually) Remove the associated files and folders from the lab filesystem.

This process is cumbersome and prone to errors. To improve user experience and streamline this operation, we should implement a method that simplifies and automates the removal of a device from the network scenario.