Revert "[NEXUS-5957] Remove "/repodata" using repository API when only one yum member" because group repositories does not allow delete operations (read only)

This reverts commit bdf327aa0fb4ba4614eaa8f8c9015446e3331165.

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>

Conflicts:
	plugins/yum/nexus-yum-repository-plugin/src/main/java/org/sonatype/nexus/yum/internal/task/MergeMetadataTask.java