[Parser] Remove `abiAttribute` experimental feature #106

Job	Run time
Validate generated code	2m 1s
Run tests using swift-syntax-dev-utils (Windows)	55m 58s
Run tests using swift-syntax-dev-utils (Linux)	23m 6s
Test / Linux (5.9 - jammy)	3m 59s
Test / Linux (5.10 - jammy)	4m 1s
Test / Windows (5.9 - windows-2022)	21m 27s
Test / Linux (6.0 - jammy)	4m 10s
Test / Windows (6.0 - windows-2022)	20m 2s
Test / Windows (nightly - windows-2019)	15m 34s
Test / Linux (nightly-main - jammy)	5m 5s
Test / Windows (nightly-6.1 - windows-2019)	15m 49s
Test / Linux (nightly-6.1 - jammy)	4m 45s
Soundness / API breakage check	0s
Soundness / Documentation check	5m 4s
Soundness / Unacceptable language check	2s
Soundness / License headers check	10s
Soundness / Broken symlinks check	2s
Soundness / Format check	44s
Soundness / Shell check	37s
Soundness / YAML lint check	3s
Soundness / Python lint check	7s
	3h 2m 46s

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