feat: revert #3400: reintroduce experimental S2A integration in client libraries grpc transport #9741

Job	Run time
build(8) except for gapic-generator-java	4m 21s
build(21) except self-service clients	13m 13s
build (11)	14m 50s
build(8) for gapic-generator-java	11m 31s
compatibility	1m 32s
build (17)	14m 53s
dependency_analyzer_unit_test	14s
lint	22s
gapic-generator-java-bom	1m 41s
showcase (11)	4m 11s
showcase-clirr	3m 11s
showcase-native	8m 28s
showcase (17)	4m 34s
unmanaged_dependency_check	5m 3s
showcase (21)	4m 11s
	1h 32m 15s

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