Revert "Maven plugins are now supported by :pom-plugins to avoid name conflict with Leiningen :plugins vector. "

This reverts commit a7f020e8c91468448b5f97c0eb88b2aac746c566.
Revert "Added support of maven plugins in project.clj."

This reverts commit ac7b3b1059d69d22a2a18f9ee5086df8680e1d74.