Inefficient memory use in UndoAfterBurner

[veprbl]

This is seen on input files with large collections of MCParticles (e.g. synchrotron radiation backgrounds at 10 GeV)

and without `MCParticlesHeadOnFrameNoBeamFX` plots by @rahmans1

[rahmans1]

First attempt at a quick fix #2175

[simonge]

I would argue this shouldn't be closed. The memory leak is still going to be there just the size easily manageable for now?

[veprbl]

I would argue this shouldn't be closed. The memory leak is still going to be there just the size easily manageable for now?

The size is under control. There was no indication that this was a memory leak. Having said that, valgrind outright crashed in one of the allocations from UndoAfterBurner on our test files, so debugging further was not practical.