Remove dependency between assemble and macappbundle tasks

[dcabasson]

Specifically remove the block:

project.afterEvaluate{
          if (Os.isFamily(Os.FAMILY_MAC)) {
              project.getTasksByName("assemble", true).each{ t -> t.dependsOn(dmgTask) }
          } else {
              project.getTasksByName("assemble", true).each{ t -> t.dependsOn(zipTask) }
          }
        }

Not all the users of the plugin might want those dependencies attached to the assemble tasks. It's trivial to add the dependency in the build if needed, but impossible to remove it as of Gradle 6+ (see https://docs.gradle.org/5.0/release-notes.html#deprecations )

Other similar plugins such as the Gradle Application plugin do not create similar link between distTar/distZip and the assemble task.