remove legacy headers from AsgTools package
A while back AsgTools was split up into two packages AsgTools+AsgMessaging. For backwards compatibility dummy headers were kept in AsgTools, but with the move to master it seems like a good opportunity to remove all those old headers and update the files that were still using them.
For the most part this was straightforward, except for AsgTools/AsgMessaging.h which included both AsgMessaging/AsgMessaging.h and AsgTools/IAsgTool.h. I fixed all cases were that let to problems in the AnalysisBase project. For all other project builds, I'll have to see whether there are problems in the CI.