Remove duplicate licenses in project/build.scala,

that results in a unusable POM (by Maven) generated and deployed in
http://dl.bintray.com/betehess/banana-rdf/org/w3/banana-rdf_2.10/0.5/#banana-rdf_2.10-0.5.pom
cf warning in:
http://www.scala-sbt.org/release/docs/Community/Using-Sonatype.html#third-pom-metadata