Stop needlessly writing to generated files.

[GriffinRichards]

Currently Porymap will write (but not read) the generated files include/constants/map_groups.h and include/constants/layouts.h. This is because the project repos do not generate these files before they are needed. After the changes in pret/pokeemerald#1949 (and after they are synced to pokefirered and pokeruby), they are generated in time and Porymap doesn't need to write them anymore.

Given that this is a breaking change (if Porymap stops writing them users will need the changes in that PR) and that Porymap continuing to write the generated files is harmless, this should wait to be fixed alongside a breaking change of more consequence.