remove unused code field from `athena_message` #787

Job	Run time
Build binaries	3m 17s
Examples	7m 44s
Test (ubuntu-latest)	2m 49s
CLI	4m 34s
Test (runs-on, runner=8cpu-linux-arm64, run-id=12599293931)	1m 42s
Test (macos-latest)	2m 28s
Formatting & Clippy	27s
Test (Go) (ubuntu-latest)	1m 18s
Test (Go) (runs-on, runner=8cpu-linux-arm64, run-id=12599293931)	1m 0s
Test (Go) (macos-latest)	1m 36s
Test (Go) (windows-latest)	4m 38s
	31m 33s

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