Use our physfs.json instead of the one in shared-modules.

This is waiting on a pending PR:
flathub/shared-modules#419

Author: ProjectSynchro

org.naev.Naev.yaml

@@ -163,7 +163,7 @@ modules:
           version-query: .tag_name
           url-query: .assets[] | select(.name|endswith(".tar.gz")) | .browser_download_url
 
-  - shared-modules/physfs/physfs.json
+  - physfs.json
 
   - name: python3-pyyaml
     buildsystem: simple