fix: mame2015 reads hiscore.dat from its cwd

hiscore_init opens the file through emu_file with no search path. The branch that built system_dir/mame/ is under #if 0, so the profile's mame2015/ path named a place the core never reads.

emulators/mame2015.yml

@@ -57,19 +57,19 @@ notes: |
   ROM naming follows MAME 0.160 conventions.
 
 files:
-  # Data files (system_dir/mame2015/)
+  # Data files
   - name: hiscore.dat
     installed_on: [recalbox]
-    path: "mame2015/hiscore.dat"
     required: false
     category: game_data
     sha1: "68e94fb579f46f3255ef7c34c0322f3f0f3c8e20"
     md5: "7e31f0b84f6ea6f9ffec0cd968decf9f"
     size: 216250
-    source_ref: "source src/emu/hiscore.c:122-138, 335-337"
+    source_ref: "source src/emu/hiscore.c:122-138, 330-338, source src/emu/fileio.c:42-67, 341-370"
     note: >-
       high score definitions, external file, not embedded. metadata/hiscore.dat of the core repository. is_mem_range reads
-      only "cpu:addr:len:start:end" lines under a "gamename:" header.
+      only "cpu:addr:len:start:end" lines under a "gamename:" header. Opened by emu_file with no search path, so from
+      the working directory of the frontend: the branch that would read system_dir/mame/ is under #if 0.
 
   # SNK Neo Geo MVS/AES
   - name: neogeo.zip