ci: Remove Docker Compose files used by old CI #81

Job	Run time
Swift 6 Language Mode	0s
Compatibility test	4m 57s
Example packages / Linux (5.8)	22s
Example packages / Linux (5.9)	15m 54s
Example packages / Linux (5.10)	14m 53s
Integration test / Linux (5.8)	22s
Example packages / Linux (nightly-6.0)	21m 49s
Soundness / API breakage check	2m 41s
Integration test / Linux (5.9)	1m 34s
Example packages / Linux (nightly-main)	28s
Integration test / Linux (5.10)	1m 33s
Integration test / Linux (nightly-6.0)	2m 8s
Soundness / Documentation check	1m 47s
Integration test / Linux (nightly-main)	30s
Soundness / Unacceptable language check	5s
Soundness / Broken symlinks check	2s
Soundness / Format check	39s
Soundness / License headers check	5s
Soundness / Shell check	29s
Unit tests / Unit tests / Linux (5.8)	25s
Unit tests / Unit tests / Linux (5.9)	1m 40s
Unit tests / Unit tests / Linux (5.10)	1m 31s
Unit tests / Unit tests / Linux (nightly-6.0)	2m 10s
Unit tests / Unit tests / Linux (nightly-main)	28s
	1h 16m 32s

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