Drop techs_researched from savegame
As noted in #44595, techs_researched serves no purpose in the savegame - it needs to be recalculated anyway to validate it. Let's drop it from 3.2 savegame format.
Keep still in S3_2 to catch possible consistentcy issues, but remove from 3.3.
As noted in #44595, techs_researched serves no purpose in the savegame - it needs to be recalculated anyway to validate it. Let's drop it from 3.2 savegame format.