fix: remove @BetaApi from ApiFutures and ApiService #5411

Job	Run time
build(8) except for gapic-generator-java	3m 35s
build(8) for gapic-generator-java	9m 36s
build (11)	13m 4s
build(21) except self-service clients	11m 11s
build (17)	12m 16s
compatibility	1m 53s
gapic-generator-java-bom	2m 18s
lint	23s
showcase (11)	4m 11s
showcase-clirr	3m 10s
showcase-native	8m 4s
showcase (17)	4m 33s
unmanaged_dependency_check	4m 1s
	1h 18m 15s

Provide feedback