remove unused Swift 6 language mode workflow #8

Job	Run time
Soundness / Broken symlinks check	2s
Soundness / API breakage check	3m 22s
Soundness / Documentation check	2m 27s
Soundness / Format check	35s
Soundness / License headers check	3s
Soundness / Shell check	30s
Soundness / Unacceptable language check	3s
Soundness / Python lint check	7s
Soundness / YAML lint check	4s
Cxx interop / Cxx interop / Linux (5.9)	2m 10s
Cxx interop / Cxx interop / Windows (6.0)	1s
Cxx interop / Cxx interop / Windows (nightly-6.0)	1s
Cxx interop / Cxx interop / Linux (5.10)	1m 59s
Cxx interop / Cxx interop / Linux (6.0)	2m 21s
Cxx interop / Cxx interop / Windows (nightly-main)	1s
Cxx interop / Cxx interop / Linux (nightly-6.0)	2m 37s
Cxx interop / Cxx interop / Linux (nightly-main)	2m 41s
Unit tests / Unit tests / Linux (5.9)	4m 11s
Unit tests / Unit tests / Windows (6.0)	3s
Unit tests / Unit tests / Windows (nightly-6.0)	1s
Unit tests / Unit tests / Windows (nightly-main)	1s
Unit tests / Unit tests / Linux (5.10)	4m 8s
Unit tests / Unit tests / Linux (6.0)	4m 20s
Unit tests / Unit tests / Linux (nightly-6.0)	5m 6s
Unit tests / Unit tests / Linux (nightly-main)	5m 12s
	42m 6s

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