build: remove unnecessary maven version mapping block

Author: matrei

gradle/publishing.gradle

@@ -8,10 +8,6 @@ publishing {
     publications {
         register('grailsMailPlugin', MavenPublication) {
             from javaComponent.get()
-            versionMapping {
-                usage('java-api') { fromResolutionOf('runtimeClasspath') }
-                usage('java-runtime') { fromResolutionResult() }
-            }
             pom {
                 name = 'Grails Mail plugin'
                 description = 'Provides Mail support to a running Grails application'