chore: Remove the remaining migrated docs #15185

Job	Run time
gapic-bom	1m 24s
owlbot-yaml	49s
root-pom	1m 23s
owlbot-py	50s
gitignore_correctness	50s
generate-readme	51s
group_id_check_for_maps_libraries	6m 34s
package_name_check	49s
	13m 30s

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