feat: revert #3400: reintroduce experimental S2A integration in client libraries grpc transport #9818

Job	Run time
build (11)	15m 8s
build (17)	14m 31s
build(8) except for gapic-generator-java	4m 20s
build(21) except self-service clients	13m 59s
build(8) for gapic-generator-java	11m 33s
compatibility	1m 50s
dependency_analyzer_unit_test	22s
gapic-generator-java-bom	2m 2s
lint	28s
showcase (11)	4m 27s
showcase-clirr	3m 14s
showcase (17)	4m 34s
showcase-native	8m 55s
unmanaged_dependency_check	8m 40s
showcase (21)	4m 36s
	1h 38m 39s

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