We somehow ended up with two copies of the same interface class.  The
problem with having two interfaces for the same task was that tools
implementing the different interfaces could not be used
interchangeably.  That specifically broke the configuration of some of
the common CP algorithm sequences, which use the same algorithm class
for all selection tools.

I was somewhat torn between which of the two classes to keep, and
while I originally wanted to keep `CP::ISelectionTool`, it turned out
that `IAsgSelectionTool` was much easier to keep.  That is because the
`AcceptInfo` and `AcceptData` classes are in the same package as the
interface class, and anybody who wants to use or implement that
interface will need those two classes as well.

One could potentially move all three classes together to
AsgAnalysisInterfaces if that is considered advantageous, but that
would be a bigger undertaking and they would all have to be moved
together.