POM: fix license-maven-plugin configuration
POM: remove superfluous description

The description inherited from the parent is fine (at least for now).
Update license and file headers

This was done using:
  mvn license:update-project-license license:update-file-header

The only real change is the loss of the legal disclaimer at the bottom
of the license. This disclaimer is not actually part of the BSD-2
license proper, but rather an addendum. For relevant discussion, see:
  https://jira.codehaus.org/browse/MLICENSE-80