Remove legacy variable usage.

library/inventory/group_by

@@ -19,7 +19,7 @@ notes:
 
 EXAMPLES = '''
 # Create groups based on the machine architecture
--  group_by: key=${ansible_machine}
+-  group_by: key=machine_{{ ansible_machine }}
 # Create groups like 'kvm-host'
--  group_by: key=${ansible_virtualization_type}-${ansible_virtualization_role}
+-  group_by: key=virt_{{ ansible_virtualization_type }}_{{ ansible_virtualization_role }}
 '''