flatpak: Deduplicate CEF from the bundle

CEF is installed in /app/cef. After OBS is built, it no longer needs
/app/cef because everything that OBS needs is copied elsewhere.

So removing /app/cef at the cleanup stage will not cause issue
and will also reduce bundle size.

CI/flatpak/com.obsproject.Studio.json

@@ -304,8 +304,7 @@
         "cp -R ./libcef_dll_wrapper/libcef_dll_wrapper.a /app/cef/libcef_dll_wrapper"
       ],
       "cleanup": [
-        "*.a",
-        "./*"
+        "*"
       ],
       "sources": [
         {