The algorithm object should only store a reference to any input
workspaces if it is told not to store in the ADS and then it
should only have a single reference by the time execution has
completed. Here we clean out internal caches of workspace pointers
that were keeping workspaces alive if an algorithm object was not
removed immediately, e.g. in the AlgorithmManager.

The AlgorithmProxy used ensure this happend after algorithm execution
finished but that no longer exists. Some workspace types require workspace
destruction to release resources such as file locks, e.g file-backed
MDWorkspaces, and keeping references to those workspaces complicates
writing scripts a subsequent operation required a workspace to be
deleted.