AnalysisTop: Cleanup of MetaData reading

This MR attempts to cleanup the code for reading various metadata. In particular, historically there are now three different sources from which AT tried to extract metadata, when in fact probably only xAOD::FileMetaData is actually needed for most of the stuff we need.

Workaround for buggy metadata in R21 samples are removed, currently we assume that the same bugs from R21 hopefully won't show up again (I might be slightly naive here).

All of the metadata is now read from FileMetaData from MetaData Tree. There is still a caveat that to determine the derivation stream, we use a rather ugly approach by looping over all branches of MetaData tree to find the branch matching a "Stream*" name pattern.

In addition, up to now, AT determined the period (2015+16 vs 2017 vs 2018) by reading a single event from CollectionTree. This was mostly for convenience reasons to clear out triggers not usable in a given period (e.g. different lowest unprescaled trigger in one year vs another year), but perhaps there is motivation to have such information available in MetaData.