This was the final piece of non-tile-related data to be in there.
.def should be restricted to existing use cases concerning setup of render data, not for game content.
.def is not the right place for this - it needs to run very early in the process, before scripted actors are loaded, so doing this stuff there means that half the initialization has to be postponed and error reporting is sub-par.
These are now part of RMAPINFO which gets parsed as one of the very last things - it is also where GZDoom is doing some of these things.
The better error reporting also allowed fixing some errors in these definitions.
