ci: remove unnecessary distributionManagement section #9809

Job	Run time
build (11)	14m 59s
build (17)	14m 42s
build(21) except self-service clients	13m 48s
build(8) except for gapic-generator-java	4m 37s
build(8) for gapic-generator-java	11m 19s
compatibility	1m 53s
gapic-generator-java-bom	2m 5s
lint	30s
showcase (11)	4m 46s
showcase-clirr	3m 17s
showcase (17)	4m 15s
showcase-native	8m 39s
showcase (21)	4m 7s
dependency_analyzer_unit_test	12s
unmanaged_dependency_check	7m 6s
	1h 36m 15s

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