remove unused code field from `athena_message` #786

Job	Run time
Build binaries	3m 9s
CLI	4m 27s
Examples	7m 17s
Test (ubuntu-latest)	2m 48s
Test (runs-on, runner=8cpu-linux-arm64, run-id=12598717070)	1m 46s
Test (macos-latest)	2m 26s
Formatting & Clippy	23s
Test (Go) (ubuntu-latest)	1m 18s
Test (Go) (runs-on, runner=8cpu-linux-arm64, run-id=12598717070)	1m 3s
Test (Go) (macos-latest)	1m 47s
Test (Go) (windows-latest)	5m 52s
	32m 16s

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