Remove <prerequisites> from pom.xml to avoid WARNING

[WARNING] The project ... uses prerequisites which is only intended for
maven-plugin projects but not for non maven-plugin projects. For such
purposes you should use the maven-enforcer-plugin. See
https://maven.apache.org/enforcer/enforcer-rules/requireMavenVersion.html

This is already done in odlparent.

Change-Id: If10668be0f69f89a0101e8fe6bf611130772a9e0
Signed-off-by: David Suarez <david.suarez.fuentes@ericsson.com>