ci: Remove migrated libraries from downstream protobuf check #17289

Job	Run time
group_id_check_for_maps_libraries	8m 8s
root-pom	1m 45s
gitignore_correctness	1m 10s
gapic-bom	1m 39s
generate-readme	1m 16s
package_name_check	1m 4s
owlbot-yaml	1m 10s
owlbot-py	1m 16s
	17m 28s

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