Re #7778. Eliminate erroneous use of AnalysisDataService.

In general, algorithms shouldn't be dealing directly with the ADS,
the Algorithm base class takes care of these interactions.
Re #7778. Remove unneeded use of the AnalysisDataService.
Re #7778. Get pointer out of property, not ADS.
Re #7778. Remove unnecessary references to the ADS.
Re #7778. Revert changes to FilterEvents.

It turns out that FilterEvents is relying on workspaces being in the ADS
before the algorithm has completed so that it can call GroupWorkspaces on
them. Probably the proper solution would be to refactor so that they are
placed directly into  a group, but I'm not going there now.
Merge remote-tracking branch 'origin/bugfix/7778_unnecessary_ads_usage'