remove unused Swift 6 language mode workflow #11

Job	Run time
Soundness / API breakage check	3m 15s
Soundness / Documentation check	2m 28s
Soundness / Unacceptable language check	5s
Soundness / License headers check	5s
Soundness / Broken symlinks check	3s
Soundness / Format check	34s
Soundness / Shell check	33s
Soundness / YAML lint check	5s
Soundness / Python lint check	6s
Cxx interop / Cxx interop / Linux (5.9)	2m 3s
Cxx interop / Cxx interop / Linux (5.10)	2m 0s
Cxx interop / Cxx interop / Linux (6.0)	2m 3s
Cxx interop / Cxx interop / Linux (nightly-6.0)	2m 50s
Cxx interop / Cxx interop / Linux (nightly-main)	2m 49s
Cxx interop / Cxx interop / Windows (6.0)	1s
Cxx interop / Cxx interop / Windows (nightly-6.0)	3s
Cxx interop / Cxx interop / Windows (nightly-main)	3s
Unit tests / Unit tests / Linux (5.9)	4m 10s
Unit tests / Unit tests / Linux (5.10)	4m 15s
Unit tests / Unit tests / Linux (6.0)	4m 37s
Unit tests / Unit tests / Linux (nightly-6.0)	4m 58s
Unit tests / Unit tests / Linux (nightly-main)	5m 22s
Unit tests / Unit tests / Windows (6.0)	4s
Unit tests / Unit tests / Windows (nightly-6.0)	1s
Unit tests / Unit tests / Windows (nightly-main)	1s
	42m 34s

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