remove unused Swift 6 language mode workflow #26

Job	Run time
Soundness / Format check	40s
Soundness / API breakage check	2m 4s
Soundness / Documentation check	1m 54s
Soundness / Broken symlinks check	5s
Soundness / License headers check	5s
Soundness / Python lint check	4s
Soundness / Shell check	31s
Soundness / Unacceptable language check	3s
Soundness / YAML lint check	3s
Cxx interop / Cxx interop / Linux (5.9)	1m 21s
Cxx interop / Cxx interop / Linux (5.10)	1m 26s
Cxx interop / Cxx interop / Linux (6.0)	1m 26s
Cxx interop / Cxx interop / Linux (nightly-6.0)	1m 41s
Cxx interop / Cxx interop / Windows (6.0)	2s
Cxx interop / Cxx interop / Linux (nightly-main)	1m 55s
Cxx interop / Cxx interop / Windows (nightly-6.0)	3s
Unit tests / Unit tests / Linux (5.9)	2m 58s
Cxx interop / Cxx interop / Windows (nightly-main)	3s
Unit tests / Unit tests / Linux (5.10)	2m 52s
Unit tests / Unit tests / Windows (6.0)	4s
Unit tests / Unit tests / Linux (6.0)	2m 46s
Unit tests / Unit tests / Windows (nightly-6.0)	3s
Unit tests / Unit tests / Linux (nightly-6.0)	3m 9s
Unit tests / Unit tests / Windows (nightly-main)	3s
Unit tests / Unit tests / Linux (nightly-main)	3m 9s
	28m 30s

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