gba release: drop _payload.c attachments

The two _payload.c files are C-array embeddings of the corresponding
_mb.gba ROMs, used for compile-time linking into a host firmware.
Submodule consumers (joypad-os) read those from the committed
gba/build/ tree, not from a downloaded Release asset. Attaching them
to the Release was just noise that gave end-users two extra "what
is this?" downloads next to the playable ROMs.

After this change the Release attaches only the two playable ROMs
(joypad_mb.gba, tester_mb.gba). CI build-verification artifacts in
verify-build.yml still include the .c files -- those uploads are for
inspecting build output from the Actions tab, not end-user assets.

Author: RobertDaleSmith

.github/workflows/release.yml

@@ -127,10 +127,13 @@ jobs:
         working-directory: gba
         run: |
           mkdir -p _release
-          cp build/joypad/joypad_mb.gba       _release/
-          cp build/joypad/joypad_payload.c    _release/
-          cp build/tester/tester_mb.gba       _release/
-          cp build/tester/tester_payload.c    _release/
+          # Only the playable .gba ROMs go in the public release.
+          # _payload.c (C-array form for compile-time embedding) lives in
+          # the committed gba/build/ tree; submodule consumers like
+          # joypad-os pull it from the working tree, not from a Release
+          # artifact, so attaching it to the Release would be noise.
+          cp build/joypad/joypad_mb.gba  _release/
+          cp build/tester/tester_mb.gba  _release/
           ls -la _release/
 
       - name: Stage release artifacts (PC Engine)

gba/README.md

@@ -144,8 +144,11 @@ unconditional handshake-complete write).
 
 Tagged as `gba-v<semver>` from the repo root — see
 [`gba/CHANGELOG.md`](CHANGELOG.md) for per-version notes. The release
-workflow attaches `joypad_mb.gba`, `joypad_payload.c`, `tester_mb.gba`,
-and `tester_payload.c` to each GitHub Release automatically.
+workflow attaches the two playable ROMs (`joypad_mb.gba`,
+`tester_mb.gba`) to each GitHub Release. The C-array embed forms
+(`build/<variant>/<variant>_payload.c`) stay in the committed `build/`
+tree for submodule consumers — they're not duplicated to Release
+artifacts.
 
 ## Origin / credits