Unused now, and arguably not a valid concept anymore.
A run control may consist of different runworkers,
'operating' on different systems.
Since the removed RunConfiguration::abi() implementation uses
only public Target ABI, user code could revive that locally
in case it was needed again.
Change-Id: I658c6e88b4a1aec18bf4de91fc86230552bc0710
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>