fix(aria2): remove --fsync=false to avoid crash on older aria2c versions

Exit code 28 (Invalid argument) indicates this user's aria2c does not
support the --fsync option. Remove it unconditionally; the stderr drain,
relaxed RPC timeouts, and increased retry coverage remain in place.

py/services/aria2_downloader.py

@@ -510,7 +510,6 @@ class Aria2Downloader:
                 "--continue=true",
                 "--daemon=false",
                 "--quiet=true",
-                "--fsync=false",
                 f"--stop-with-process={os.getpid()}",
             ]