chore(o11y): remove beta api from observability classes #19108

Job	Run time
bulk-filter	1m 4s
windows	2m 48s
lint	3m 35s
enforcer	2m 10s
gapic-libraries-bom	2m 17s
generation-config-check	1m 47s
changes	3s
split-units (sdk-platform-java, 8)	2m 19s
split-units (sdk-platform-java, 17)	2m 21s
split-units (sdk-platform-java, 25)	2m 4s
split-units (sdk-platform-java, 11)	2m 4s
split-units (sdk-platform-java, 21)	2m 9s
units (8)	1m 41s
units (11)	1m 18s
units (25)	1m 18s
units (21)	1m 11s
units (17)	1m 13s
	31m 22s

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