Java Buildpack 2.1

Starting with the 2.1 release of the Java Buildpack, packaged versions of the buildpack should not be linked via submodule.  Instead, a packaged version of the buildpack, (complete with version baked into the code) should be used.

This change removes the existing Java Buildpack submodule and replaces it with an exploded packaged version.  In addition, the `buildpack_java` package was updated to cope with the lack of a git directory (the git hash of the package is baked into the version).  Finally, the package `spec` was updated so that it includes all files since the packaged buildpack is already as minimal as it can be.