Build: fix version sorting

Prevents us from incorrectly thinking the current version is
the bwc version.

buildSrc/src/main/groovy/org/elasticsearch/gradle/Version.groovy

@@ -24,7 +24,7 @@ import groovy.transform.Sortable
 /**
  * Encapsulates comparison and printing logic for an x.y.z version.
  */
-@Sortable
+@Sortable(includes=['id'])
 public class Version {
 
     final int major
@@ -60,10 +60,6 @@ public class Version {
         return "${major}.${minor}.${bugfix}${snapshotStr}"
     }
 
-    public boolean equals(Version compareTo) {
-        return id == compareTo.id
-    }
-
     public boolean before(String compareTo) {
         return id < fromString(compareTo).id
     }