feat: revert #3400: reintroduce experimental S2A integration in client libraries grpc transport #9738

Job	Run time
build(8) except for gapic-generator-java	4m 6s
build(21) except self-service clients	13m 23s
build (11)	14m 33s
build(8) for gapic-generator-java	11m 16s
compatibility	1m 29s
build (17)	14m 48s
lint	22s
dependency_analyzer_unit_test	14s
showcase (11)	4m 20s
showcase-clirr	3m 2s
showcase (17)	4m 28s
gapic-generator-java-bom	1m 55s
showcase (21)	4m 38s
showcase-native	8m 44s
unmanaged_dependency_check	5m 10s
	1h 32m 28s

Provide feedback