fix: read each europe-only region tag in its code

Region tags must name the territory the code selects a file for. Each
entry tagged europe alone was read at its pin: PAL branches Australian
media reach now include oceania, and tags that follow a video standard,
a user setting or a hardcoded value are removed.

emulators/md-emu.yml

@@ -124,7 +124,7 @@ files:
 
   - name: bios_CD_E.bin
     system: sega-megacd
-    region: [europe]
+    region: [europe, oceania]
     required: true
     agnostic: true
     size: 131072