Remove crosschain leftovers #7413

Job	Run time
e2e_post_etna	11m 14s
Unit (macos-12)	8m 35s
Unit (ubuntu-20.04)	6m 55s
Unit (ubuntu-22.04)	6m 44s
e2e_pre_etna	11m 28s
Unit (windows-2022)	13m 25s
Unit (custom-arm64-focal)	12m 41s
Unit (custom-arm64-jammy)	11m 44s
Fuzz	13m 27s
Protobuf Lint	5s
e2e_existing_network	4m 18s
Lint	3m 18s
Upgrade	3m 13s
Up-to-date protobuf	32s
Up-to-date mocks	2m 4s
Up-to-date go.mod and go.sum	15s
Build Antithesis avalanchego images	8m 25s
Image build	11m 21s
Build Antithesis xsvm images	12m 13s
	2h 21m 57s

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