Revert "[maven-release-plugin] prepare for next development iteration"

This reverts commit 2dd1e8f8613b7fab409ed8c72b70c48539d54904.
Revert "[maven-release-plugin] prepare release spark-parent-0.8.1-incubating"

This reverts commit 15c356c362529347ea87b95e7a6008e0391faceb.