Recently I encountered a situation where a plugin was bringing in a version of a jar file that was causing my application to misbehave. In order to fix this issue I had to remove the errant jar file from the final build. This is the code that you can use to do that. You have to place this code snippet in your BuildConfig.groovy. Hope this helps someone else.
grails.war.resources = { stagingDir ->
delete(file:"${stagingDir}/WEB-INF/lib/<name>.jar")
}