Remove identity.version from login-server pom

Use project.parent.version instead, which already contained the value

 [#71195408] https://www.pivotaltracker.com/story/show/71195408
Simplify pom

Eliminate redundant properties. They appear to cause issues with the
versions-maven-plugin.

[#71195408] https://www.pivotaltracker.com/story/show/71195408