Revert "Merge branch 'JetDecorators_190729' into 'master'"

This reverts merge request !25234 (merged), following the discussion on ATLASRECTS-5322. The MR in question was creating warning messages in q-tests, which turned out to be due to jet modifiers being run before the collection is recorded into StoreGate. This makes the WriteDecorHandles used in the modifiers unhappy (though interestingly, they seem to produce the right results regardless). Fixing this issue requires a fairly substantial re-design of the jet reconstruction algorithm, which we're coincidentally in the process of doing anyway. So, we'd like to revert these changes temporarily until we have a solution worked out on that side.