ci: remove nexus-staging-maven-plugin #18242

Job	Run time
owlbot-py	1m 11s
owlbot-yaml	1m 6s
generate-readme	1m 11s
gapic-bom	1m 49s
group_id_check_for_maps_libraries	8m 30s
gitignore_correctness	1m 16s
root-pom	1m 44s
package_name_check	1m 6s
	17m 53s

Provide feedback