[Workload] Remove server-groups

What's the problem?

Although there is code for provisioning server-groups, the targeters and nemesis are not aware of them and consequently do not make use of them.

This introduces technical debt into the project as the code which provisions the server-groups is occupying space in the code base but is currently not bringing value to the project as it's not being 

What's the fix?

As the server-groups are of low priority, they can be removed (MB-45602) and reintroduced later (MB-35760).

This issue tracks the removal of the command line options and the removal of the code that relates to the provisioning of the server-groups.