chore: [vertexai] remove BetaApi annotations for GAed features (#10605) #10512

Job	Run time
gapic-bom	1m 38s
owlbot-yaml	29s
generate-readme	30s
consolidate-config	1m 30s
gitignore_correctness	25s
group_id_check_for_maps_libraries	3m 5s
owlbot-py	36s
package_name_check	27s
root-pom	1m 37s
	10m 17s

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