refactor: drop the archived platform status

RetroPie was the only platform with status: archived, which kept it out
of verify --all, slots, the pipeline and list_platforms unless
--include-archived was typed. release_pack already decides which packs a
release publishes and the installer serves every platform, so the status
set nothing apart. The field, its schema entry and the flag are gone, and
RetroPie is covered by every full run like any other platform.

scripts/diff_truth.py

@@ -215,7 +215,7 @@ def main() -> None:
 
     if args.all:
         platforms = list_registered_platforms(
-            args.platforms_dir, include_archived=True
+            args.platforms_dir
         )
     else:
         require_platform(args.platform, args.platforms_dir)